I think he was just bitter that he wasn’t asked to return, even though union issues prevented him from doing so. He even went as far as to say he didn’t want Arcelus dating his daughter! Ouch!
I think the union issues were actually what he had a problem with. He likely didn't appreciate 4Kids' decision to make their TMNT a non-union production, as that's usually associated with lower pay and fewer benefits compared to union ones (it's worth noting that the vast majority of western-produced cartoons are fully unionized for at least the voice actors, compared to many anime dubs which are not). So he probably wasn't only upset about being replaced, but with said replacement being willing and able at the time to work for reduced pay and benefits, which could be seen as devaluing his profession. That all said, I don't think the personal attacks were warranted and I think he could have handled the situation a bit more professionally.
