If there were a coup here in the US, let's say the January 6th brigade succeeded, then they changed the US Constitution, would we then immediately start trusting the next set of elections? Or would we rightfully see that as fruit from a poison tree? That's Mearsheimer's point, you don't have to agree with Putin's response to accept that it was the obvious and inevitable response from our actions meddling in Ukraine.
Try this analogy - If I walk up to Mike Tyson at a bar and start talking shit to him, spitting on the ground, taunting him and challenging him should I not expect him to punch me in the face? Wouldn't most people acknowledge that I had it coming, even if it was unnecessary and disproportionate to my actions? Does pointing it out mean I'm tacitly approving of his actions, or am I just being logical and saying if you mess with a bull you will get the horns?