Scientists and science fans around the world will take to the streets on Saturday in a show of support for facts and reason.

And like the myriad reasons people go into the sciences themselves, marchers planning to head to the main March for Science event in Washington, D.C. or satellite marches around the world have a wide number of reasons for getting involved.

The march, which is unprecedented in modern U.S. history, was triggered by the Trump administration's frontal assault on everything from actual facts to funding for climate, health and energy research. But more broadly, there is a sense in the U.S. and elsewhere that science's central role in society is in jeopardy. Actual facts are giving way to, well, "alternative facts."

And scientists are not going to stand for this any longer.

"We need more support for science — not less! ... I hope the March for Science will cause not just politicians but the average American to take a deeper look at how important science is and how much we need to keep funding scientific advances in all fields," rocket scientist Michelle Lucas said via email.

Other researchers are marching because their livelihoods are directly threatened by Trump's plans to cut funding to many major science agencies in the U.S.

At the moment, government-funded science in the United States is facing unprecedented cutbacks and uncertainty as the White House plans to gut everything from the Environmental Protection Agency (EPA) to the Centers for Disease Control and Prevention, and the Department of Energy.

"Not only is it threatening the career path that I’ve chosen and what I've chosen to work on and what I eat and breathe and bleed for every day," Jane Zelikova, a scientist who studies the impacts of climate change, said in an interview.

"This administration is threatening the very core of me."

Science under attack

If Trump's budget blueprint is enacted, it would cut funding to the EPA by at least 31 percent, slashing thousands of science-related jobs and taking away grant money from many scientists dependent on it.

Trump administration officials have also expressed anti-science sentiments including denying the reality of human-caused climate change and questioning the efficacy of vaccinations.

"I think that measuring with precision human activity on the climate is something very challenging to do and there's tremendous disagreement about the degree of impact, so no, I would not agree that it's a primary contributor to the global warming that we see," EPA administrator Scott Pruitt told CNBC in March, when asked if carbon dioxide is the main "control knob" on the planet's climate.

"But we don't know that yet, as far as... we need to continue the debate and continue the review and the analysis," Pruitt said.

The truth is that the vast majority of scientists — including researchers at Pruitt's own agency, agree that human activity is the main cause of climate change, so any "debate" about whether global warming is real or not has no true basis in fact.

The March for Science is designed to make it clear to leaders around the world that scientists are a large and influential group of people that should have a voice in politics. It is also aimed at motivating supporters of science and the scientific method to get involved in the political process, and see that they have a large stake in this too.

In other words, this isn’t just about fighting against impending layoffs or funding cuts: It’s about fighting an all-out assault on the value of science and its place in our democratic society.

Astrophysicist Neil deGrasse Tyson expressed this best in a video he released on Wednesday, warning of the consequences if America and other nations turn away from scientific inquiry and lose their grasp on facts.

"We hold our leaders — both in science and in politics — accountable to the highest standards of honesty, fairness, and integrity," reads part of the March for Science's goals. "We gather together to send a message: We will all work to ensure that the scientific community is making our democracy stronger."

Politicization concerns

To honorary co-chair of the March for Science Bill Nye — of "Bill Nye the Science Guy" fame — this march represents an opportunity for scientists to help get their voices heard when it comes to decision-making in the United States.

Nye's dream is that the march will force lawmakers to enact policies based on scientific fact, not emotion, or denial.

"The march is to remind lawmakers and the world how important science is in our everyday lives," Nye said in an interview.

The March for Science itself hasn't been without its own controversies, though.

As the idea for the march was gaining traction in the scientific community, scientists were speaking out about how the march could politicize science, making it harder to get their voices heard if science is seen as partisan.

That argument against the march doesn't resonate with Nye, however.

"To pretend that science is not political is to not be paying attention to how governments around the world are run," Nye said.

"Science enables innovation no matter what country you live in, and so innovation is what keeps countries competitive and in the game economically around the world."

Self-inflicted wounds

As noble a cause as the science march is, it has also been characterized by a host of major fumbles, primarily concerning the inclusion of marginalized voices in the science community.

A fair number of vocal supporters of the March for Science — and some of the organizers behind it — have claimed that diversity and the issues faced by scientists of color should not be emphasized in this march.

"The organizers’ public communications have bungled through various diversity statements. Communications have reinforced stereotypes that exclude minority scientists," sociologist Zuleyka Zevallos wrote in a Minoritypostdoc.org blog post analyzing the diversity messaging of the March for Science.

"The organizers’ have made light of the gender pay gap in science and the structural barriers that inhibit women’s careers in science. The Washington D.C. organizers have also played into an infamous case of sexism in science, while the Los Angeles organizers engaged in racist dog whistling, suggesting that allowing minorities into the march would lead to violence."

According to Nye, this march isn't actually about diversity in science — even though science, on the whole, is dominated by white men, something that can be traced to oppressive systems that make it difficult for women, people with disabilities, people of color and other people of diverse backgrounds to enter the sciences.

Posts to the Twitter hashtag #marginsci get into the nitty gritty of how the March for Science has done a poor job of representing the interests of a more inclusive group of people.

.@UCBerkeley @katiejmbaker Women disproportionately work in equity & diversity; hired or volunteering to fight against a system that doesn't want to change. #marginsci — Dr Zuleyka Zevallos (@OtherSociology) April 8, 2017

If the organizers’ goal is to ensure that science remains a public good for all of us they must be willing to take a stand against injustice https://t.co/WfJPFLu6jp — Millie Copara (@MiraclesCopara) April 20, 2017

#ScienceMarch reminds us that we have lots of work to do, and that work is already being done by #marginsci. Everyone else? Show. Up. — Jacquelyn Gill (@JacquelynGill) April 16, 2017

"We can't solve all the problems all the time," Nye said. "This is a march for science. It is not, to me, a march for diversity in science."

If the March for Science is about all scientists, doesn't that mean it should be representing the interests of — and above all advocating for — those scientists of diverse backgrounds?

The March for Science is scheduled to take place in at least 517 separate marches around the world on Saturday, with the largest event taking place in Washington.

Maria Gallucci contributed reporting to this story.