NATO has been on the Russian Federation’s borders as long as the RF has existed.

And it was on the borders of both the USSR and the RSFSR as long as NATO has existed, which is considerably longer.

This argument is dumb because Estonia and Latvia are already on their border.

There's nothing NATO can do with Ukraine they couldn't already do with the Baltics.

It's more than dumb. Russia's current actions are actually only now making NATO presence in the region tangibly stronger (see: Sweden, Finland). This wouldn't happen without Putin invading Ukraine.

The difference is whether or not you're on the open plains leading to Moscow. The eastern edge of the Carpathian Mountains has always been a hard line for Russia, going back to the middle ages, because once the plain to Moscow opens up, it's nearly indefensible. That edge is in eastern Ukraine.

It's a very 19th/20th century view on 21st century geopolitics, but hey, that's modern Russia for you.

And Lithuania, bordering Kaliningrad which is a - highly militarised - Russian enclave bordering Poland and Lithuania.