According to who? Please cite a specific court case where a judge ruled that calling for the boycott of Israeli products was deemed illegal.

If such a ruling was later appealed and eventually overturned, then of course that would not count. But a judge ruling on a case is technically the only way something can be considered provably "illegal" in the US.

I realize that you want to believe there are certain inalienable rights that somehow no longer exist, but I do not believe that to be the case. The courts exist for a reason, and just because people are sometimes arrested or charged with things that are not actually legal, that doesn't mean it won't later get thrown out in court, and it doesn't mean that your rights have disappeared.

Even if all of that did happen, such a case would most likely be appealed to the Supreme Court and ruled unconstitutional.