I've never found Mearsheimer's arguments on Ukraine all that convincing. I really liked Adam Roberts succinct take down in the Economist a couple weeks ago. I know Roberts doesn't address all Mearsheimer's points, but he hits the main ones
I'm being super generous when I say he's splitting hairs.
Take this part:
"These factors suggest that the 2008 proposal to expand NATO to include Georgia and Ukraine is just one among many developments that have made the current crisis so acute. It is arguable, indeed likely, that the NATO expansion proposal made matters worse, as may some other Western actions, but to assert that “the West is principally responsible for the Ukrainian crisis” goes too far."
Or this gem:
"It’s questionable whether Mr Putin was right to say NATO posed a threat to Russia’s sphere of influence. From the start in 2008 there were different interpretations of what was meant by “will become members”. "
Putin made it very very clear where he stood, and yet you still see armchair psychoanalysis being done. It's all pretty shoddy. There is certainly nothing of substance here that even begins to address Mearsheimer's iron-clad arguments.
I wouldn't say Roberts's arguments are splitting hairs, I'd say he's turning the whole thing around and saying Putin interpreted every Western action in the worst light possible, Russia decided that Ukraine was its domain, and the West and Ukraine had the right to define their own relations.
Mearsheimer's argument boils down to: Russia thinks it has the right to do what it wants in Eastern Europe, and the West caused this problem by not saying "ok."
Putin violated the Bucharest Memorandum by moving into Crimea and eastern Ukraine. Russia created this mess.
You are arguing like the man whose wife wants to divorce him, and who concludes that the only way to stop the divorce would be to give in to every demand his wife ever makes, which is clearly unacceptable. Every marriage counselor will tell you: What escalates conflict is not so much “not giving in“, but “not listening“. Mearsheimer’s argument, in other words, is not that West needs to do everything Putin ever says. Instead, his argument is that the West is provoking Putin by treating him as if he is not to be taken serious, and as if Russia as a country is not to be taken serious.
Putin wasn't even scared of NATO coming to the defence of a sovereign country, Ukraine. It's damn sure not he was never scared of NATO actually threatening Russian territory.
I see too many people these days being reflexively contrarian, like they're on a next level of understanding, simply by being opposite of the "current thing." Mearsheimer's arguments are widely known, it's not an "aha" moment to name drop him, stick to the arguments. Personally, I prefer info from people that actually predicted the invasion months ago.