Apart from trying to call a historic champion of minorities "scum and filth" (oh, and "scumbags"), he also said they needed to pay a "much higher amount." But of course, he didn't say what would make him happy, probably because this is purely about irrational contempt for the SPLC more than anything.
First, that's not vengeance so much as making people pay for the wrong. Technically that is the definition, but the way almost everyone uses it, vengeance is an overreaction.
Second, just because they have history does not change the harm they have done. Cosby was a great inspiration, but it does not reduce the fact that he is a rapist. Just because the SPLC has done great things in the past does not change that they smeared people and held their ground until they were sued. As I said, what the SPLC did literally made his life more dangerous. It undermined the important goal he was trying to reach, and for what?
What the SPLC did was horrible. I would bet that the majority of people at the SPLC are not bad, but there was someone that very much lied and when she was told of this, held her ground. That is on the SPLC because they were made aware, and said they agreed with the list.