> Why is this different? It feels like there are lots of business situations where you essentially give up a right as part of a contract.
It isn't different, in your framing, but there are lots of policy reasons why we wouldn't want the state to coerce or compel speech. Especially political speech, as the case is here. And the text of the 1st amendment and years of jurisprudence make freedom of speech different than other rights (just as 5A due process is different than other rights, etc.)
We mostly recognize that it is generally a bad thing for the government to make you say things, unless there is a very good reason to do soon (like, you must label your food products with nutrition info) [0].
To reframe, imagine the government made you sign a pledge that "Abortion is murder" or "Abortion is great, everyone should have one" instead. Or imagine a law that says "All contracts are voidable, if you (a business) and your employees and your outside contractors must not participate in a boycott of Israel." That law might reach extremely far (too far?) if the company is Walmart (~2.3 million employees) and Walmart wants to do business with your state (it does) and Walmart is asking you to sign that pledge to now do business with them.
So, the question is -- if instead of forcing you to say something, and threatening you with jail, is it okay for the state to just refuse to deal with you (as an incredibly powerful market participant). Some will say "That's pretty clever lawyering on the part of the state to do that," while others will be a little more unsettled, thinking if the state can do this, what else can they do?
[0]: https://en.wikipedia.org/wiki/Compelled_speech#Examples_curr...