A mounted bicyclist at a walking pace has a lower cross section than a parent with a stroller or a person in a wheelchair. Sidewalks are multi-modal, until we can get rid of the scourge of cars, anybody opting not to use them should be encouraged as long they're being civil.

Try testing that theory. If you walk your bike in a crowd, the crowd will pack in the space around you very efficiently. If you ride your bike at walking speed, the crowd will give you quite a wide buffer zone. You are less predictable, and most bikes at that low of a speed are very wobbly. Thus you talk less space walking your bike despite the wider cross section.

This isn't true in my experience. I have ridden through areas like this often, because for some reason my city put one of the main bicycle routes through a busy pedestrian tourist area, full of families and inebriated diners.

If you dismount and push a bike, people get struck by pedals and handlebars. The rider has to allow much more space to prevent people walking right into them.

Riding at walking speed, some pedestrians may give a bit of space, but most of them don't alter their movement in any appreciable way. A capable rider has better control of a bicycle when they are actually riding it, and can keep pedals away from shins even in close proximity.

Nobody is riding their bike in a crowd mate

Then the objection I'm replying to is also irrelevant.

It's not, bikes fit in sidewalks just fine