Dr. Seuss: Even if we take your assumptions as true, these are still the facts: There are laws against segregation (by race, sex, etc.) of public accommodations. By entering in a franchise agreement with a public transportation service, you are agreeing to these abide by these laws. If you believe these laws violate your constitutional rights, then you can challenge them. To break the law without applying to the appropriate legal channels, citing the Constitution as your justification, is not a feasible legal practice.
The Constitution and its amendments are not quite as unilateral as you believe them to be. It is the job of the Supreme Court to interpret the Constitution and determine constitutionality. If things worked as you are arguing, then what exactly is their function? By your logic, gay people would have no problem marrying, as per the interpretation of several different amendments. What right would any state have to abridge theirs? That’s why we have the court system and legal action – to regulate unrestrained behaviors under the protection of the Constitution.
A conflict between established state/franchise law and the tenets of the Constitution would definitely warrant investigation. Perhaps the law would be determined in our favor. Who knows? My point is not to say that separate seating is wrong, but to emphasize the need for the issue to be addressed in the proper manner. If there are laws and we break them, then the Constitution cannot be valid. Plus, isn’t the current method causing a chillul Hashem? Why not try to avoid that?
My comment on this practice being an established tenet of Judaism did not relate to legal semantics. I was just wondering whether or not the issue warranted such extreme action on our end. As pointed I mentioned before, some buses are segregated left-right as opposed to front-back. This practice is ostensibly not as discriminatory as the current one is, so if the government is applied to appropriately, there is very little reason for this not to be allowed.
Oh, and I would be very interested in hearing some cases where private entities were allowed to violate a(n) individual/group’s constitutional rights. As well as the provenance and basis of this practice. That would surely make for an interesting legal precedent…