No one has been arguing against proactive censorship, but while Facebook took the time, money and manpower to do it properly, Tumblr took a shotgun approach and shot itself in the foot. People are against the absolutely disgusting way Tumblr enacted a blanket ban that was haphazardly done without solving any of the real problems.
Here's the thing - When the nsfw content ban came in, the bot was so poorly coded that it was a joke at what it was marking as nsfw. Someone did an experiment where they took a photograph of a
Raindrop Cake and made copies of it in different hues and shades - One normal, one blue, one green and the third pink. Of the four images, one got tagged as nsfw. Care to guess which colour? Hint, rhymes with "think". Because the bot was only checking for certain shades of colours. Not shapes, not words, not tags, just colours. Which ended up with a lot of content inaccurately being tagged as "nsfw" and accounts/blogs getting warnings, despite the fact that they contained no nsfw content.
But let's continue with some of the other problems with Tumblr, shall we? Like the pornbot problem that is infesting that website. I stopped using it in 2016 and it was a major problem then and from I understand, the problem has gotten worse. To the point where the only concentrated effort to get rid of them wasn't by the staff, but by organised groups of users reporting those bots. Because that right there is proactive censorship. And it wasn't done by the staff.
Moving on, the vast majority of blogs that have been affected by the adult content ban has been the LGBT community, with many blogs suffering from the false positive of the NSFW bot. These weren't porn blogs and they certainly weren't filled with nsfw content. They were often blogs where people could go to gain a measure of sex education in a community that is woefully underrepresented by the mainstream. It
was a safe place for the LGBT, something rather lacking on the internet these days.
And never mind that the "female presenting nipple" that led the way in Tumblr's sledgehammer approach to censorship has the umbrella effect of covering breast-feeding, mastectomies and gender reassignment surgery. So that's new mothers losing another resource to help them learn how to take care of their child, cancer patients losing another place where they could continue their recovery and trans-individuals losing another place where they could be comfortable with becoming the real them.
Then you have the fact that while adult content might be bad, extreme right wing and white power blogs remain untouched by Tumblr's new policies. Because apparently nipples are far more dangerous than fascism and racism.