“Let me state boldly; I am against sexual assault. But…”
“I am against revenge porn. But…”
“I am not a supporter of crime or criminals.…”
Of course you are against all the bad things. So you don’t need to say it. Please don’t.
I understand the impulse: if you publicly oppose uncritically believing people who make rape accusations, you will be accused by small-minded people of favoring sexual assault. If you publicly oppose criminalization of anything, zealots of criminalization will accuse you of favoring that thing. If you defend people accused of crimes, the booboisie will infer that you support those people and their crimes.
The disclaimer is a preemptive strike against this illogical inference. But even if it’s true, it is not going to convince anyone. (If your disclaimer is, “I am a strong proponent of free speech, but…”, it’s probably not true; the second half of your sentence will tell.)
The great mass of readers are either too poorly educated to tell the difference between procedure and substance, or too dishonest to acknowledge it. The ignorant group doesn’t understand that you can fight criminalization without supporting bad conduct; the dishonest group understands, but pretends otherwise in order to quash dissent. (I’m sure you all have favorite examples of the latter, you misogynistic rape apologist you.)
This is our culture: subtlety is lost. Ignorant people may be educable, but you can’t make dishonest people honest. (Protip for telling them apart: you can’t. So you get to pick between trying to educate the dishonest, and giving up on the ignorant.)
By proclaiming your bona fides, you play into this cultural trend. You go on the defensive before you’ve been irrationally attacked. Even though you don’t mean to, you lend legitimacy to the illogical inference, opening for discussion whether you are in fact in favor of revenge porn / sexual assault / crime, when you intend to discuss how best to deal with revenge porn / sexual assault / crime.
If it goes without saying, don’t say it.