I agree, it doesn't look like there is much [objectivity] in this concept.

If you don't go looking for it, you won't find it. As is so ofen the case on LW, that door has been shut without even trying to see what is behind it.

I see no reason why "forbidden" in the moral sense should be objective

Try explaining to someone that something they like should be forbidden because you don't like it.

Okay. "If you don't stop, I will shoot you."

Arbitrary rules enforced with threats of violence is not an optimal outcome for me.

If you have an option other than

a) subjective laissez faire where serial killers are allowed to do their own thing

or

b) Tyranny

I'd be glad to hear it. I know I have.

But seriously, WTF? Is that supposed to be an argument that if something is morally forbidden to one person it should be the same for another person?

Of course. No one should murder. I'm surprised you find that surprising.