Editor's note: Diane Ravitch is a historian of education and the author of the best seller "The Death and Life of the Great American School System."

(CNN) -- A few days ago, I wrote an opinion piece for CNN.com explaining why teachers in Wisconsin -- and throughout the nation -- are angry, and it isn't just because Gov. Scott Walker asked them to pay more for their pensions and health-care benefits. They are angry because of the unwarranted public vilification that has been heaped on them for the past two years.

The response was unlike anything I have ever seen before, and I've been writing about education for 40 years. The column received more than 8,000 comments and more than 38,000 Facebook shares. I personally received scores of emails. The overwhelming majority came from teachers, who simply wanted to say "thank you" for showing them the respect they deserve.

But about one of every 10 that I received came from dissenters complaining that teachers have an easy life, that their benefits are too generous, and that unions are selfish and greedy. A few were venomous and suggested anatomically impossible feats. One writer insulted teachers with this: "The majority of them have degrees in education, which are basically paths to baccalaureate degrees for people too stupid to get through degree programs in math, science, engineering, or even business."

CNN.com commenter "26thirdstree" wrote: "If the teachers don't like it they can quit. The fact is the teachers unions in this country have been bilking the taxpayers for years." Another went so far as to suggest that all the teachers should be fired and replaced by anyone who wanted their jobs. Well, that would surely improve education!

Anyone who has spent much time in schools today knows that it is not easy to be a teacher, especially when so many parents are missing in action. Teachers today face tough challenges: Some of their students have parents who are incarcerated or absent, some stay home while their parents look for work, some have varying degrees of disabilities, some don't read or speak English, some live in neighborhoods infested with gangs and violence, some of their students arrive in September far behind others in their grade.

Opinion: Reinvent unions, don't gut them

I hear from teachers all the time. They tell me about overcrowded classrooms, about how their school hasn't had an art or music teacher in years, about how they buy supplies out of their own pockets, about stabbings and funerals. This is not the age of "Leave it to Beaver."

As for pension and health-care envy, it is a sad thing when working Americans complain that someone else has benefits, instead of agreeing that everyone should have coverage for their health and old age. It reminds me of an old Soviet joke where a peasant says, "My neighbor has a cow and I have none, I want his cow to die." We should not join in this race to the bottom.

Here's a comment from CNN.com reader "feholder": "The real story in Madison is not about fed-up teachers. It's about gluttonous unions who don't realize the world has moved on." So, it is important to point out that the public sector unions in Wisconsin have already agreed to all of the governor's financial demands. Without any negotiations, they agreed to raise their pension contribution from less than 1% of their pay up to 5.8% and to more than double their contribution to their health care from 6% to at least 12.6%.

"SarahInTexas" says: "Employers all across the U.S. are cutting salaries and wages .... Teachers or any other public workers should not be exempt from this reality." Teachers don't believe they are exempt. Sunday, Mary Bell, president of the Wisconsin Education Association Council, said, "Money issues are off the table." Public employees "have agreed to Gov. Walker's pension and health care concessions." This is a controversy in which there are no more financial questions to be resolved.

Roland Martin: Unions have to make concessions

The only remaining issue is whether the unions will be permitted to bargain on anything other than wages -- such as working conditions -- whether pay raises will be limited by a pre-set formula, and whether unions will be required to hold annual votes on whether they should exist.

In other words, Walker talks budget, but his real goal is to bust the union and eliminate it as a force in Wisconsin politics. What this means, if the governor's bill passes, is that the only organized force that protects and defends education spending in the state of Wisconsin will be neutralized.

If the union is reduced to political roadkill, the forces of privatization and educational austerity will have their way in Wisconsin. They will cut and cut and cut some more. Who will oppose them? This will not be good for the future of Wisconsin.

Unions do not by themselves guarantee high educational achievement, but they certainly assure that adequate funding will be available to keep class sizes reasonable and to provide programs and services that children need. Without adequate funding, academic progress is unlikely to occur.

Certainly other organized interests will continue to be heard in Madison, but not teachers or others who work in the public sector.

If the voices of their teachers are silenced, who will stand up for students?

The opinions in this commentary are solely those of Diane Ravitch.