If they’re afraid of that, they joined the Fedi with a fundamental misunderstanding of how its supposed to work.
Yeah I was about to say, sure this isn’t ActivityPub, but the specific implementation of the federation should be an impolementation detail the user should never care about. You joined a federated system. Your content gets federated. Period. Whether said federation happens through ActivityPub, AT, some bridge system or the Binford Content Disperser 5000XL+, that’s really not the point of any discussions so long as the content does get federated.
The same exact people will whine about how Bluesky should have been using ActivityPub in one second, and bitch about how they don’t want their content bridged over there in the next. It’s almost as if they haven’t thought this through.
Of course anyone is free to join an instance that blocks the bridge - that’s part of the beauty of the whole system.