Letting a megalomaniacal dictator that has clearly lost command of his senses run amok, especially when in control of a large nuclear arsenal is a risk we can not really afford, and appeasing such a person will only feed into the cycle of demands.
But what exactly do you propose?
this is bullshit. NATO is not expanding, NATO is not the actor that is able to perform that action, rather it's emergent property of sovereign countries choosing to join NATO.
So who is Putin to tell what sovereign countries can or cannot do? If he's so unhappy with a choice that sovereign country is making with regard to joining a defensive alliance, maybe he should offer something better instead and not behave like a crazy lunatic dictator?
There is nothing valuable in "look at it from Putin's perspective" argument when his perspective is tyrannical.