>You're mixing up what's happening and what you find justifiable.

The issue is that you are the one mixing things up. Your presenting Ukraine and Russia as equally being able to stop the war. But stopping the war for Ukraine would mean losing their sovereignty, while stopping the war for Russia would have no impact on their sovereignty.

>If your plan is to keep telling Putin to end the war - it doesn't seem very productive.

We can keep telling Putin that while we send military aid to Ukraine and sanctioning Russia, if Ukraine keeps being successful then Putin is more likely to listen.

>Escalating that can make things less popular, and make the war seem more necessary from the Russian perspective.

Support for sending troops to Ukraine was around 35-40% at the start of the war. It seems pretty obvious that main reason NATO troops aren't in Ukraine are due to Russia's nuclear weapons (as noted here and here).

Doesn't this also show Putin that NATO doesn't want to attack Russia, since this would be the perfect opportunity to perform such an attack?

>They probably made a calculation that the risk is low enough.

You hit the nail on the head. The risk of conflict escalation is low when sending aid, because NATO is not directly involved. Sending troops to Ukraine would massively escalate the conflict, as pointed out by the Biden admin.