We all will lose if any side of the conflict starts the war. For Poland this may mean, for example, a refugee crisis on the scale far beyond what we had after conflict in Syria. I do not think this will happen.

As for the expansion of NATO, any change in the military configuration of it is an unnecessary and significant escalation. Russia is not threatening neither Finland, nor Sweden, not even close, but we will get at least an arms race in Baltic region if they join. Russian military strategy is that of active defense, they build up the power to protect their own territory. They do not have capabilities to attack and occupy Poland or Finland for a long time, mainly for logistical reasons (their army will run out of fuel quickly and won’t be able to resupply fast enough). The worst part of the expansion is not that there’s a hypothetical risk of a conflict but that it strengthens Putin. He has built his rule on the idea of Fortress Russia surrounded by enemies. Any hostile moves by the West help him to build this case and to prove that pro-Western opposition is wrong. But if instead we could bind Russia in the series of multilateral deals with its neighbors, including defense cooperation, we could on one side defeat the Russian hawks and on the other side create too big pie to lose for Russian elites. America has Monroe doctrine: we should try to remove the need for Russia to have one. Situation in Ukraine made this really hard to achieve, but not impossible.