Try explaining to her about the case of some gay men in the middle east using the website discreetly who run the risk of death after this leak: https://news.ycombinator.com/reply?id=10084651 (citing a reddit post).
And, if you are comfortable putting her in a precarious position, you should ask her if she honestly knows of any of her girlfriends who have cheated before. Or, more simply, if any of her girlfriends are not single and have a Tinder account. I've noticed the "shoe on the other foot" has silenced many of the Twitter camp.
For me there are only two honest responses:
A) "I can understand that vigilantism of this kind can hurt innocent people is therefore wrong"
B)"if needed, the innocent should suffer so that those who I dislike are ruined".
The latter position can be dressed up in all kinds of fancy words "bad people must be brought to justice no matter what". Stripped down to its core, however, and barring the exceptional circumstances, I would say that the desire for street-justice is pretty much evil. So far as I can tell, the rationale for position B is full throttled emotion: "I [want to] hurt the people I don't like and I [want to] kill the people I hate. Doing that makes me feel good, so it is good."
Needless to say, I stay as far away from those who subscribe to position B, as humanly possible.
And, if you are comfortable putting her in a precarious position, you should ask her if she honestly knows of any of her girlfriends who have cheated before. Or, more simply, if any of her girlfriends are not single and have a Tinder account. I've noticed the "shoe on the other foot" has silenced many of the Twitter camp.