Collude
When you collude with someone you secretly plot together to do something bad.
OK, let's work with this definition. First, is collusion illegal? No, not in and of itself. One could collude to do something illegal, but since plenty of "bad" things are not illegal, collusion itself isn't illegal either.
So did Trump Jr. collude with the Russians? Clearly some people believe so, but that's not an open and shut case either. One has to establish that what they were doing was bad, and that's not actually trivial.
But what
were they doing? The Russians promised to provide information damaging to Hillary. Had they done so, would this have been bad? For Hillary, sure, but it's not axiomatically true that this would have been bad for the public. If it was, for example, evidence of Hillary doing something illegal (like approving that uranium deal in exchange for money), then arguably making this information public might be
good for the public. If it was naked selfies of Hillary, then publishing them would be
bad for the public.
But as far as we can tell, no information actually changed hands. So there's not much to evaluate for goodness or badness. Whether you think he
would have done something bad with the Russians becomes largely a matter of whatever your pre-existing view of Trump Jr. is. But it appears that things never reached the point at which Trump Jr. was even in a position to determine whether cooperating with the Russians was a good thing or a bad thing.