But you're saying the ICE agents can slay anyone they like without any personal repercussions.

No. As pointed out upthread, they can't slay anyone they like. Rather, state laws - even murder laws - can't stop them from carrying out their duties. If their duties require them to slay someone, the state law can't restrain them.

That doesn't mean an ICE agent can go find their ex-wife and shoot her for personal reasons. That's not part of the exercise of their duties. It also means that state law can apply in circumstances when it wouldn't stop the officials from fulfilling the duties of their office. So a state law that says that it's murder if you shoot a prone, unarmed man in the back ten times is probably one that the courts would hold does not conflict with federal agents fulfilling their objectives.

But it does mean that you can't use state law to to make it harder for ICE to perform their functions the way Philip was suggesting. If the rule actually limits their ability to do these raids in any material way, then the rule has to give way to the federal objective.