Not agreeing is one thing, but it is a remarkably easy decision to understand - people go to WWII because every single war since then has been a disaster for US interests and outcomes (I think every single, certainly most). The last time the US had an unambiguous win by fighting was 70 years ago when they got involved in a fight very late. Since then all the warmongering has made America poorer, they don't achieve anything good and generally make the US worse off.
They made a call that they don't trust the military industrial propaganda and they want to see some peace happening for once. Pretty solid decision too; if we can all have normalised relations with the US after Iraq then we can stomach Russia misbehaving in Ukraine. Escalating a land war in Europe is stupid and its been a mistake every other time the Europeans tried it; even in WWII where they claim to be justified. The blood-lust left everyone closely involved broken and it'd have been better if they found a more peaceful route to ending the violence. The fact that they failed to negotiate something doesn't mean it was impossible.