1) "we" (the US) are not hitting the Russians, "we" (Europe including the UK) are providing them with weapons for their self-defence, since it is in our interest to prevent a humanitarian catastrophe happening on the Polish border. I am no longer clear what, if any, assistance the US is providing. It is also very important in this that no NATO or EU forces are engaged directly with Russian forces yet, despite persistent incursions into EU airspace and occasional sabotage operations in Western Europe.
The UK is developing special US ITAR-free missiles for this purpose: https://www.thedefensenews.com/UK-Develops-Three-Low-Cost-Lo...
2) "start talking realistically about what behaviour is tolerable": I think we're past the point of pretending that international law applies evenly, and back to Mao's "power comes out of the barrel of a gun".
If we go back to a Cold War multipolar world between China, the US, Europe, and Russia, the only one of those which hasn't made public statements threatening European territorial integrity is China.
(at this point I would expect India to start asking whether they get to be a world power or not and what they're going to do with that, too)