For me there, in terms of bikes on pavements, a few different issues.
One is where cyclists cycle quickly on narrow pavements, where young children (and or the elderly / hose with mobility problems) can come out of their houses / front gardens unseen - there have been some horrendous collisions and this is the worst and most dangerous form for me. Speed, and weight of bike / person added to no warning for either party makes this really bad. I’d be happy for severe punishments for people who do this.
You then have cyclists cycling quickly on other types of pavements where visibility is better. This can still be dangerous, again for the same groups.
And then you people cycling more slowly which is less dangerous.
All the above are wrong, but to different degrees.
You read or hear quite often that some people will not cycle on the road as they are scared to do so, don’t feel comfortable. Finding a solution to that would stop some people - safer and more cycling lanes and maybe more (or better advertised) cycling on the road type lessons (I think Lewisham and others used to run some?).
You’ll always have some people who just don’t care - they will be the same on a bike, scooter, car etc but if they can become a real minority will be easier to target, and of course the less of them the less potential for accidents.
Finally adults with youg children - I’ve no issue with this myself as long as they are cycling reasonably slowly. Where possible though the adult should be on the road or walking, though it’s not always possible.
I don’t find there is one particular group that is worst than others, it’s pretty mixed but some ‘groups’ always get highlighted.