I thought reddit was great until I saw the monetization of speech push discussion in a different direction: first with corporate astroturfing, then by paying people to conduct psyops.
I thought Facebook was pretty great until I realized that anything I post there is visible by people who I might not want to see it- I think of the uncles who unironically post about how "monkey is suddenly a racist word", but also "influential people saw this post that I made five years ago that might have been funny five years ago but definitely isn't now" (read: James Gunn).
I thought Instagram was pretty cool until adverts and the realization that you only see the positives of people's lives through the filter they operate, and that it affected how I felt about myself!
This isn't to say that everything we're producing is bad. We now have cheap, readily available sources of reliable knowledge that update quickly (encyclopedias take a year and were pretty pricey, by comparison). I also think functions like online banking and simple government actions (think re-registering your car) seriously extend our ability to operate in society.
But I'm finding that the honeymoon phase of the next big internet product is all too sweet- The first six months is generally okay, then we find a few edge cases of malice, followed by the real underbelly as bad actors take over the platform.
Also, for someone who says "I don't think that's to say I shouldn't be worried about it", you sure seem to take a liberal - maybe even a bit contradicting? - stance not wanting to be too idealistic about it.
There was a case once where a software project amended the GNU GPL with a no military use clause... On that note, you can never tell exactly who your customers are, and you shouldn't fit technology with a built-in kill switch or have it call home, which is just the worst of all options, as seen with several unpopular videogame companies.