While I agree that it's not a good idea, I can answer that last question:

The idea would be that when an American enforcement body, presumably the FBI, determines that a bunch of cash or whatever was stolen by Russian hackers, the treaty compels the Russian government to keep records of the hackers' activity, and it "creates frameworks for collaboration, including mutual legal assistance and extradition". So instead of saying "hey, you stole all our money" and getting the response "wow, it must suck to be you", we could make them give the money back and extradite the criminals.

Clearly not enough people oppose it, because five eyes has been a thing for decades, and isn't going anywhere.