I've not legitimised the invasion. NATO and others have by not being prepared to use our own nukes. NATO have taken the path of physical appeasement from the start.
It's now very clearly that the West collectively failed to understand Putin and it's led to this. We must learn from this.
Taiwan will probably be next. Because the precedent is being set that as China has nukes nobody will fight them directly.
Interestingly, the growing view is that China is now much less likely to attack Taiwan after seeing the level of sanctions levelled as Russia.
It's not a matter of giving up. It's a matter of being practical. In your mind can Ukraine win? If so, what does winning look like?
I think if you're right and Ukraine have no chance, then your argument is rational (even if I find it repulsive on an emotional level) but I don't think it's clear that Ukraine has no chance. Russia is bogged down and taking heavy losses, meanwhile the international reaction is battering their country. A peace deal that secures most of Ukraine's goals is a plausible outcome.