I think he's just trying to circumvent the karma system

"Just".

People are welcome to abandon an account when they realize they have irrevocably destroyed their reputation and wish to start again and try not being an asshat. They are not welcome to use multiple accounts to subvert the karma system.

I agree it's Dmytry, but not a sockpuppet.

Please review the context. You will notice that gwern is arguing with two 'people' in this discussion. Both of them, by your own prediction, are Dmytry. Using multiple accounts to support each other in a single argument is exactly what 'sockpuppetry' is all about. To put it mildly: I don't like it.