Lately there's been an anti-porn push among the younger, right leaning internet crowd. Part of this is a reaction to the addiction to sex and fetishes many on social media seem to have, but it also is fueled by theories about pornography corrupting minds (with some evidence). Andrew Torba of course is good at latching onto trends and opportunities in that crowd even if he can't implement them whatsoever, just look at the idea behind Dissenter or announcing services after ban waves.
The problem is, being anti-porn also contradicts being a free speech absolutist. Tumblr crashed and burned because of the porn ban, and when Twitter does (there's already
fears of this) it's going to lose users as well. Torba doesn't want a Twitter alternative (but pro free speech) as much as he wants a right-wing hugbox, and this stunt is hard proof of it.