Tumblr has long housed some of the most self-expressive, marginalized communities of the internet. The site welcomed LGBTQ and sex-positive bloggers, artists and creators, self-proclaimed nerds and those in need of support.

Now, with a strict and poorly executed ban on adult content, Tumblr is alienating power users and pushing some to other sites.

The blogging site, owned by Yahoo parent Verizon, announced earlier this month it would flag and remove "adult content" — most instances of nudity and erotica, with some exceptions for artistic or educational content. On Monday, the first of the flagged content was taken down.

"The thing that is so upsetting to me is that I see all of these people, most of them young people, who are trying to find a place where they can be themselves, where they can find people who are like themselves," said Wil Wheaton, a writer and actor. "And Tumblr is kind of taking that away by de-listing and hiding these things."

Wheaton has been on Tumblr for more than a decade and has watched as communities formed. Trauma survivors turned to Tumblr for relief, he said, and young artists found a sympathetic audience.

"Those communities took care of themselves. They did a really good job of policing themselves and caring for their members," Wheaton said.

He also watched as groups of white supremacists and misogynists formed at the margins of the site. Tumblr communities raised alarms about the groups, Wheaton said, but Tumblr turned on its core instead.

"You don't burn down the village to save it," Wheaton said.

In a blog post this week, Tumblr acknowledged the transition had been rocky and vowed to improve its systems.

"Tumblr has always been home to marginalized communities and always will be. We fully recognize Tumblr's special obligation to these communities and are committed to ensuring that our new policy on adult content does not silence the vital conversations that take place here every day," the company said.