This has been an accepted thing since more or less NATO's inception, NATO and American intelligence, and pretty much everyone else, have recognized that this is a threat to Russia. Now, after the invasion, it's become a taboo.
This isn't an excuse for Russias behaviour, or in any way a moral absolvement. Say you have a criminal organization that operates in an area, and the cops decide to expand their presence there, of course that's a threat to the criminals; it's harder for them to operate the way they want to when more law enforcement is around.
A few months ago Russian soldiers were in Nicaragua for a training exercise, and the American government stated that they viewed this as a provocation. Nicaragua is of course not a threat to American security, neither is a miniscule Russian presence there, so if we are to accept that America views this as an issue, of course increased NATO forces closer to the Russian border is.
I'm trying to be as careful as possible here, because some people tend to be very sensitive to what they see as Russian apologism. It doesn't mean that Russian aggression is in any way justified, it doesn't mean that NATO should reject countries wanting to join, it doesn't mean NATO shouldn't deploy more troops and equipment closer to the Russian border as a response to Russian invasions, it doesn't mean that NATO expanding in the direction of Russia implies that nations aren't joining on their own volition. It means that Russia will view this as a threat, because of course they will.