I agree with your statements at large, but considering Uber was not aware of any active investigations, they're under no obligation to assist police in enacting a sting.

I'm not suggesting that it is, as there are semantically many problems with it, but an argument could be made that this is more of an extension of one's fifth amendment rights to remain silent than it is evading the law. Starting a company to drive people around is (depending on one's interpretation) either presumptively legal or presumptively illegal. Let's assume that many people view it as the former. Is it silly to assume that Uber might have anticipated the Portland government's assumption that it was the latter?

What if it were considered legal in every municipality worldwide except for Portland? That doesn't make Portland wrong or right, but at the same time, it doesn't make Uber wrong for the assumption that someone might find it to be presumptively unlawful.

I think that there are plenty of valid reasons to hate Uber, but anticipating a law enforcement response to something Uber deemed presumptively lawful seems like a pretty rational set of actions.