If you can convince yourself that a proxy war will lead to WWIII then you can convince yourself of anything
"If you convince yourself that a war with will lead to a war with allies of the enemy country, then you can convince yourself of anything"
"If you convince yourself a fire near a forest can spread to the forest, you can convince yourself of anything."
not everything is a slippery slope scenario, but that doesn't mean there are none.
Russia is fighting tooth and nail because we have ripped all control away from them, and if we take anymore its likely to make them feel backed into a corner. This may be a stuffty situation, but we cant make a bad situation worse.
The last thing we need is to repeat history by basically creating a neo-treaty of versailles.
The only difference here is that this would be a silent agreement that would only last a few days at the most.