I don't think there is an inalienable right not to be offended. Offence being so subjective, there would be no practical way to enforce such a right. What if I were to take offence at hearing Republican politicians speak, for example?
The concept of offence crept into this thread in the context of significance - - was there any real significance to a breach of the anti-establishment clause, or was it something of no real consequence? And as far as I can see, there are at least two arguments that would take the breach out of the "inconsequential" category - - the "slippery slope" argument and the "offence taken" argument. And I think the "offence taken" argument was taken up by default without too much thought, because the "slippery slope" argument lacks any real immediacy and is so highly speculative.
But I'm not sure where you are going with this. Because if I don't have a right not be offended, does that mean that you do have a right to offend me? I think it's gotta go deeper than offence. To that extent, you do have a point.
Why don't we go back to the basics - - what was the point of the anti-establishment clause in the first place? The framers valued liberty, including liberty of conscience. They didn't want a state church, which would be likely to shut down competing churches and thus force men to worship in a way or to a god they did not want, at the same time preventing them from worshiping in a way or to a god that they DID want. This must have been highly obnoxious to the framers. But WHY? What's the big deal if I, for example, am required by law to go into a church, get down on my knees and pray to Jesus? Where's the harm? I would still believe in my heart of hearts that it's all a bunch of malarkey. So what's the big deal?
The fact is, to a guy like me, there IS no big deal. I'm not a believer in very much, I don't think God would give a shit one way or the other if I pretended to give in to a fake religion and worship their fake gods. He'd understand all along that I really believed in him, even while I pretended to believe in the monkey or whatever the fuck they were worshiping. Wasn't a big deal - - I'm small potatoes, a nobody in the cosmic scheme of things, I couldn't make God any bigger by worshiping him and I couldn't make him any smaller by worshiping the monkey. So the anti-establishment clause couldn't have been intended for guys like me - - it had to have been for the benefit of the True Believers, the guys who give a shit, who'd put their lives on the line for the "honour" of their religion. That being the case, the anti-establishment clause must have been made for the purpose of not giving offense to those who give a shit - - the religious ones, the True Believers. Don't force them into somebody else's church, because for them it IS a big deal. And don't turn their workplace into a shrine to somebody else's god or church.