Many turned on you.

Yeah, I noticed that and it is regrettable. I think some people are on edge, but that doesn't really justify things. I've been on the receiving end of a few dogpiles here, and it's always been frustrating, because it's not really due to anything other than some users assuming you mean the worst, and then digging their heels in.
I also think some users on this instance feel inundated with a surity that they are on "the right side of history" and therefore they do not need to ever examine their own ideology. It's frustrating. Many of these people are Marxists, yet self-crit us something they only think they should do when they get dogpiled.

It is dehumanising.

In retrospect I can see how I completely misphrased my viewpoint. It is dehumanising, you are correct. However it is not the people killing the royal family doing the dehumanising, it is the system which they exist in itself. From the moment those kids were born they were royals, and that fact made them into something other than people. That other thing cannot exist without being a threat to a democratic society.
I think Robespierre stated this argument quite well against king Louis:

Louis was the King, and the Republic is established. The vital question that occupies you here is resolved by these few words: Louis has been deposed by his crimes. He denounced the French people as rebels, and to punish them he called upon the arms of his fellow tyrants. Victory and the people have decided that he alone was the rebel. Consequently, Louis cannot be judged. Either he is already condemned, or else the Republic is not absolved. To suggest that Louis XVI be tried in any way whatsoever is to regress toward royal and constitutional despotism. A proposal such as this, since it would question the legitimacy of the Revolution itself, is counterrevolutionary. In actuality, if Louis can still be brought to trial, he might yet be acquitted. In truth, he is presumed innocent until he has been found guilty. If Louis is acquitted, what then becomes of the Revolution? If Louis is innocent, all defenders of liberty are then slanderers. . . .

...

The trial of Louis XVI? What is this trial if not an appeal from the insurrection to some tribunal or assembly? When the people have dethroned a king, who has the right to revive him, thereby creating a new pretext for riot and rebellionÑand what else could result from such actions? By giving a platform to those championing Louis XVI, you rekindle the dispute between despotism and liberty and sanction blasphemy of the Republic and the people . . . for the right to defend the former despot includes the right to say anything that sustains his cause. You reawaken all the factions, reviving and encouraging a dormant royalism.

...

Regretfully I speak this fatal truthÑLouis must die because the nation must live. Among a peaceful people, free and respected both within their country and from without, it would be possible to listen to the counsel of generosity which you have received. But a people that is still fighting for its freedom after so much sacrifice and so many battles; a people for whom the laws are not yet irrevocable except for the needy; a people for whom tyranny is still a crime subject to disputeÑsuch a people should want to be avenged. The generosity which you are encouraged to show would more closely resemble that of a gang of brigands dividing their spoils.

Makhno and the greens.

I did not bring that up to argue who was good or bad, but to show that his idea of anarchists just suddenly being put in front of a wall is sectarian. I will again point out that the framing of the reds being oppressive as opposed to the makhnovosts is sectarian as well. Makhnovia had a secret police, political repression and persecution as well. It was war, it's necessary. I will not go into a discussion of makhnov versus the Soviets, it's just gonna be pure sectarianism and we will gain nothing from relitigating conflicts from a century ago. I'm sure you didn't intend any sectarianism on your part.
I brought up makhnov and alluded to Spain in order to highlight that people were executed as result of fighting against each other. It was not some sudden turnabout, it was the result of one side losing a conflict both participated in.
Either way being hung up on these events from a time before we were born seems very counterproductive to me. As I've already pointed out, it's not tied to some leftist infighting conflict, the only one I've ever encountered that mentioned that connotation is you.

The language was too open.

While I agree it is not specific, I'd like to point out that is a meme. It's not supposed to communicate more than a thought, not an entire concept. It is posted on a leftist forum, and it is assumed you can somewhat interpret its meaning on your own. It's not supposed to be taken 100% seriously, not everything has to be serious all the time. It's meant as joke for us and a threat towards those harbouring a transphobic sentiment.

violence is necessary.

Yea, at times. I don't think it should be glorified, but I don't think that sentiment is black and white either.