There are plenty of things that are rightly decided at state level. That doesn't mean it's OK for states to undermine the rules the populace (via their duly elected federal representatives) have chosen to make law at federal level. (And in any case it would be practically impossible to set immigration policy at state level, given that we don't have any intranational border control).
Where in the black letter law does it say that ICE are allowed to arrest US nationals?
What does that have to do with anything? If you believed some ICE officers were making illegal arrests (presumably you know their arrests are perfectly legal, since I can't see why else you'd bring up "black letter law"), the remedy for that would be to bring charges for wrongful imprisonment, not to take it as an excuse to obstruct or attack other ICE officers.
>What does that have to do with anything?
You do realize that this entire discussion is about an American citizen and an elected official no less (and not the first one) arrested by "ICE" (we don't really know who those folks are because they won't identify themselves), right?
Are you that removed from reality that you can't parse the title of the discussion in which you are participating?
This is the most extreme version of the anti-states rights argument and effectively claims the California legislature shouldn't exist.