Doesn't mean he has to like it. Wouldn't it annoy you if you've come up with a concept, but the only way to get it recognized is by dumping it down and kiddying it up?
Personally, as always, I am pretty sure the creator cares less about what a company did with his creation than his fans do. If they truly hated the idea, they shouldn't have signed off on it, and if they didn't know, then they should have. A cartoon in the 80's wasn't going to be serious, and especially for the time, if it were a cartoon it was going to be for children.
Not to mention Laird was speaking about the sale of the Ninja Turtles, and really, he didn't seem to care about the old series that much, all he said is it "wasn't what [he] would have done." and that the new series was closer. He also went on to say that Nick probably wouldn't have done what he would either, but that it didn't mean any of these incarnations are necessarily bad, just not what he would have done.
And still I say, that the old cartoon was far better than the new one--and not for it's campiness or comedy. The new series is just poorly done, and if Laird has that as his original intention for the Turtles well... then I'm sorry, but I am glad it was ripped out of their hands and placed in someone with more competency; because the cheese level is off the charts and there is absolutely nothing likable there (except for an oddly catchy theme song.)
So every time someone asks these questions "Wouldn't you hate it if you were a creator and..." I have to respond "No, I wouldn't. In fact I probably wouldn't care at all--and neither do they." The creator of Batman probably didn't hate the campy Batman, Stan Lee probably isn't rocking himself to sleep at night in a puddle of his own tears over Spider-man 3, it's just not what they would have done.
Artists/creators/writers treat these things differently than fans, and even if something disappointments them, it doesn't infuriate them. (Unless you're Alan Moore.) In Laird's case I am sure he understands that he owes a lot to that TV show, and probably even uneasily respects it, which is why he's continued to stay on despite the series staying child oriented for quite sometime.