I don't think he singled out dear little SpongeBob but no other cartoon characters. But even if he did, it would be a stretch (at least for me) to conclude that Dr. D. is saying SB is gay. He's just decrying the USE of SpongeBob for the purpose of furthering the homosexual agenda.
I read in a another article that SpongeBob's creators envision all the characters as being basically asexual. However, apparently they don't mind his being used in that video to promote "diversity and tolerance" toward homos.
Actually the more I think about it, the issue for me isn't tolerance, because I'm a pretty tolerant person... I try to treat everyone the same and I don't discriminate against homosexuals. What I object to is teaching children to think of homosexuality as perfectly normal. It isn't normal or natural. It's abnormal, and teaching children that it's normal is a lie. I think we can agree on that, right?