This is an important point. Bitcoin holders are not dumb, ETF holders maybe are not as informed. But they would surely take note of the stink kicked up by holders should some large economic nodes (i.e. institutions) start being stupid. ETFs are also businesses. The best ways to go out of business are to loose the confidence of your customer or destroy your product. Trying some softfork stupidity would do both. Miners are also not dumb. They would surely forsee the stupidity of institutional soft fork attempts and the risk they posed to their profits. I'm not saying all this couldn't happen, it just doesn't seem likely imo.