I appreciate the sentiment, but I think this is very problematic in the case of DNS, because it is so important as a backbone of communication.
(I am by no means a networking expert. My understanding is that while people can run DNS servers of their own, they still must ultimately register their domain name somewhere.)
First, I worry this will increase Russian users' exposure to monitoring and censorship by the regime. After all, if all foreign DNS services do this, Russian customers will have no alternative but Russian DNS services, which will be far more vulnerable to control and/or infiltration by the government. Won't the government be able to tap local DNS providers to see which IP addresses are looking up dissident sites? Won't it be able to track who is looking up email address domains? Perhaps who is sending what emails to who?
Helping people obtain DNS service _outside_ Russian jurisdiction seems more damaging to the Putin regime.
Second, communication is of particular importance in its nature, even when some of the parties are abhorrent. Communication enables and fosters debate and learning. It provides access to alternative sources of information, of particular importance in a propaganda state like Russia. DNS is basically a phone book that enables contact among parties, right? If all DNS providers take the view of Namecheap these Russian parties are thrown out of the phone book. There is no communication with them, no exchange of ideas or information, no possibility of reasoning with them or changing their mind.
It is in the nature of communication that sometimes the people you are communicating with are fascist militaristic assholes. Even if we could reliably determine who those assholes are (I grant, right now it's pretty clear), cutting them out of the conversation entirely doesn't seem good for anyone. The assholes can't learn what they're doing wrong if they aren't talking to anyone else. And sometimes (again, unlikely to be this time) it turns out that _we_ are the asshole.
Third, it isn't clear how bright these lines really are. I grant, right now it's quite clear that Russia is a bad actor. But what about about China, with its treatment of the Uighurs and Hong Kong? Or the US with its invasions of Iraq and Afghanistan? (Which, btw, I supported.). Or Israel, Iran, Pakistan, India -- about any one of which someone could (and does) plausibly argue is engaged in crimes against humanity. Once we start kicking people out of the "you can talk" club, we'll be endlessly arguing which people to kick out. Better not to start.
It won't do to say, "they can get domain name service from someone else". If _all_ providers take this position, these players are out of the conversation. And if this is the right position, all providers _should_ take this position.
I deplore what Russia is doing in Ukraine and hope its invasion fails. I hope the Putin regime collapses to be replaced by a truly democratic one. And I'm all for economic sanctions generally -- stop buying Russian energy, stop banking transactions, stop buying their goods. By all means, stop helping Russia finance its invasion.
But communication is a special case. I think this kind of exclusion is contrary to human communication, and potentially bad for Russian dissidents. I hope Namecheap will reconsider.