So, I haven't read the entire agreement, but the "release of unknown claims" sounds to me like:

"You agree that if Bill Gates comes up to you tomorrow and offers you $1B, you can't get out of this. You also agree that if you read a post on HN about our investors being crappy that you can't get out of it. If those events/data were known to you at the time of signing this, you wouldn't sign this document. However, you're saying that you accept the risk that you might find out some information that would have made you not sign this."

In some ways, that makes sense. When doing business dealings, you often don't have information that if you did have would alter your decisions.

I'm not a lawyer, but the difference between this release and a "general release" would be whether discovering information not known by you at the time of signing can let you out of the contract. I remember my partner (who is in law school) talking about a contract where one party had withheld information that would have materially changed the second party's likelihood to sign the agreement. I don't actually remember how the court ruled on it.

In this case, it's possible that the producers of the show might have sent around emails saying, "this team's idea is pure crap, but we need to fill the time." Knowing that might change whether you want to sign up since, if the producers think it's crap, there's a greater possibility that the investors on the show will as well. This also feels a bit on the deceptive side of things. They're withholding their opinion of the team and by doing so it makes the team more likely to sign.

I wouldn't go on some VC reality show, but I think it's partly motivated by the fact that they must deal with lots of different people and some of those people might think it good to sue if they get jilted on the show. As a counterpoint to a deceptive scenario, we could see a suit where the team alleged, "If I had known that none of the investors were interested in X-Industry, I would never have come on the show. They were from Y and Z-Industry and if I had known that, I wouldn't have given away 2% of my company." The retort could be, "well, we can't have investors from every industry and often investors invest in things outside their core". In this scenario, ABC was trying to do good - introduce a team they liked to investors who might branch out into their industry. The ABC team might have believed in good faith that the team was awesome and would persuade the investors. However, the knowledge that the investors were from a different industry might change the team's decision on the contract. Nothing was withheld in a deceptive manner, but it was still data that might have changed the team's decision.

In terms of being able to waive rights, some you can and some you can't. For example, in my state, if you have your own private entry/egress, you can waive your right to have the landlord do snow removal. At the same time, there are many things that renter's can't waive their rights on. Sometimes laws are written as a default. It's important that we've decided a way that this is handled in the absence of some explicit agreement to the contrary. However, other times we genuinely want to establish a floor past which one cannot go. I don't really know a lot about California law.

Again, I wouldn't go on some VC reality show and maybe I'm reading this wrong, but it doesn't sound too outrageous unless I'm missing something. I'm with you - I like dealing with low-key people with sound dealings. However, I don't think people like us are the types that the title conjures up. "Shark Tank" sounds like it's for people looking to make a big bang and get their way - possibly even if it means lawyering up and going after ABC. I'm not trying to defend ABC - I wouldn't agree to be on this show - but this might be reasonable if it's just about making sure that they don't have to worry about people saying, "but I never knew X and if I had known X I wouldn't have signed this" where X is something that wasn't withheld in an intent to deceive, but rather one of the millions of variables that change our decisions. Or maybe ABC is trying to be able to be deceptive and covering themself. I guess I haven't watched the show so I'm not sure what the environment is like.

EDIT: A concrete example (based on on Wikipedia). Right now, Mark Cuban is listed on the show. You want to be on the show because you think Mark Cuban specifically would like your idea. ABC is in contract negotiations with Cuban for the next season. He might not be on the show. Then we get into a big thing of going through emails. Emails show that Cuban was threatening to leave. They didn't tell you that. They reply that it's just part of his hard-ball approach to get the best contract and that they didn't think it was actually going to happen. Seems like a nightmare.