I do think there's precedent that it's self defense to fire on an unidentified stranger who knocks on your door or tries to arrest you without showing ID, but you need to make it to court to press that defense and I can't say it's a great strategy for that reason
As for why law enforcement isn't taking sides, it's because doing so would basically be the start of a state succession attempt, and would bring federal agents in to take over the state. Some states have claimed they are willing to do that in certain situations (Alaska has said in the past it will use state troopers against government if they try to enact certain gun control laws), but no one is willing to go there yet. The best they can do now is categorically refuse to assist the feds.
I mean, if masked, unidentified people are kidnapping other people, what prevents _other_ masked, unidentified people to attack the kidnappers?
Where this goes, as I understand it from my European heritage, is that you are _already_ in a situation where there's a strong incentive for an active resistance force to appear.
ICE is clearly working as both an oppressive force, and as an incitement to violence. There have been precedents in history. It never ended well for _them_.
If you're referring to why a civilian milita isn't spinning to to stop them, that's because there are (basically) two groups of people in the US. The type that are strongly pro gun, pro militia, and have knowledge in both are generally actually supportive of this particular case, and furthermore wouldn't act anyway unless they or people they like were directly targeted. This is an unfortunate cultural aspect of the US, and correcting it would have a lag time of many decades. Furthermore, the groups that did attempt to correct it got crushed by the federal government for a few decades (see the MOVE bombings, and the Black Partners history), so are extra behind. However, spinning up a small militia for directly opposing this may happen. It would look similar to the CHAZ, but that requires a large group of dedicated and motivated people to spontaneously group together.
If someone unidentified, masked, showing no warrant, no legal justification of anything, kidnaps/attempts to kidnap someone, how are (organised) citizens not in their legitimate right to retaliate, according to what their local state allows them to?
Similarly, why/how are the law enforcement units not taking side against those kidnapping?
I mean, in my country, this would obviously call for immediate intervention of the police, but maybe that's because I'm still in a country where administrative enforcement is still ultimately under the control of the judiciary branch.