I'd say that since the whitepaper it's known that 51% of the hashpower can break some of the guarantees of Bitcoin (double spend protection, censorship resistance) and that with enough hashpower, someone could try to enforce new rules on Bitcoin.

The traditional response to this has been: we'll change the mining algorithm or our nodes will reject your blocks. As far as I know, Bitcoiners have never accepted the idea of freezing or confiscating people's coins or arbitrarily saying that some already existing utxos don't count -- and such suggestions (if anyone had the audacity to make them in the past) were met with the understanding that they were an attack.

So, I would say we are not always in the situation where some portion of the community gets to decide whether our transaction is going to be counted. We may be in a position where some portion of the community decides whether new kinds of transactions (eg. Taproot, Segwit) are valid, but we have never accepted a change intentionally seizes other people's coins.

One of my conceptions about the way bitcoin works is that any coin can always be spent with the same set of rules under which it was received. This is as important as the 21 million supply cap. I'd like to believe that these basic principles of Bitcoin are not always up for grabs in the same way that the size of the op_return going forward might be.

Could some portion of the community try to push for a change to the supply cap? Yes. Are we always in a situation where this could happen? I don't believe so.

Perhaps I should have instead written: