It's not true, otherwise signs that say "no shirt, no shoes, no service" would be illegal. You're referring to laws against discrimination based on race, sex, or disabilities. This says nothing about refusing service to people for other reasons, such as a rowdy bar patron or someone who violates Terms of Service.

It's generally understood that refusing to do business with someone for political reasons, unless the person's politics involve genocide or something, is against the social contract. Not illegal, but generally not approved of by anyone (unless you have the whole US media playing the mccarthy card against the person, apparently).

I think there are many people who, given the chance, would not do business with WikiLeaks (on the grounds that their actions are perceived to be against the US national interest and potentially putting lives in danger). So I'm not sure where you're getting the idea that this would be "generally understood ... to be against the social contract."

If you're a small business and people can take their money elsewhere, that's one thing, if you're one of two giant corporations providing a vital service, that's another.