Its not about just their current taxes. Its about systemic change that democratic socialists gaining a foothold might create. The very wealthy would be made to pay for social programs and this would cause them to lose some of the obscene wealth they've hoarded.
At this point, spending some money to prevent this from happening is just financial risk management. It's their fiduciary duty.
You're getting downvoted but the way they coordinated internally to make sure Bernie Sanders would lose the presidential primary in 2016 told me everything I need to know about the Democratic party: they don't actually want liberal policies implemented. Their apparent dislike of Mamdani is further evidence.
I think that in most jurisdictions, it wouldn't be legal to take someone's gun and then shoot them with it. Once they'd been disarmed, they may no longer pose a threat. However, if you pulled out your own gun and shot them, this would be self defense, as they were still a threat when you attacked.
Morally, I think many religions claim they're objective and say that killing is wrong. However, they often carve out exceptions.
My own subjective morality in this case would agree that this is immoral, as the robber has been disarmed. However, its impossible to be sure they're really no longer a threat.
It's fun to pee at full power, but that's how you end up with a varicose vein in your testicle.