Implicit in your argument is that the outcome of political violence is always (or at least often) a net positive for the public. Not really buying that.
As the saying goes, the three boxes are the soapbox, the ballot box, and the cartridge box. This has been understood on a basic level for as long as democracy has existed.
It's four boxes, you have (unironically?) omitted juries. And democracy existed long before 19th century US politics.
If you think someone is about to begin a revolution because they saw someone post a crying guillotine on a political meme forum, then there were much deeper problems afoot than the hungriest little guillotine.
Because you didn't address it, my point remains. I am not saying someone is going to start a revolutions. I'm saying that things like your meme contribute to an environment that normalizes violence as a solution to political problems. None of the nuance of what you said above is connoted in the OP, and as with most memes, the majority of people upvote and keep scrolling.
You don't have any control over what "good political violence" means to the people for whom it is normalized. All you can control is the decision not to post the meme about how beheadings are good.
You should just say ahead of time that your beliefs are based on an interpretation of critical theory and loosening the actual definition of violence. It'll save a ton of effort for the people who don't want to bother with you.