You can't blame them can you? He did betray their trust in him. If he was disillusioned and it must have taken some time, he should have told them way earlier.
They have to punish him and send a message of sorts to other potential defectors. But anyway why is he asking for donations? Surely he can afford 3k, can't he? He's not paid peanuts but considerably more as an MP alone, and there's bound to be other jobs he does and earns because of that position.