I would hardly consider “one or two trump supporter in two years” a silo, like how many other people you encountered that were less extremists and more capable of dialogue?
Also, lemmy is not immune to tech propaganda, since it cannot be taken in isolation: people will still (albeit probably less intesively) biased by consuming other media, and being mostly a link aggregator rather than a generator of original content, there will still be some bias from the sources. It’s just a place where there’s no omnipotent algorithm so the problem is less grave, but still present.
What prevents them for doing the same? Not doing their job until they are fired so they don’t have to quit. I would get that would be even more shameful