Agree, with the addition that Kasparov is operating something like an attorney, zealously advocating for his client, or in this case, against his opponent. We shouldn't do what he says, but his voice is the purest anti-Putin sentiment in the world, and has been for a long time.

Regarding nuclear brinkmanship, I suspect that a purely rational actor will lose: the nuclear thug will take some, then take some more, and each time the rational actor will acquiesce to avoid nuclear war. This will result in the nuclear thug taking over the world, piece by piece. Ergo, it makes sense to risk nuclear war, or at least convey that you're willing to risk it, because if you don't you lose.