Not licensed here, but I do have third party property insurance. Many here are licensed too.

I'm not sure what licensing cyclists would do other than overburden the authorities responsible for managing the process. Not sure what the license authorities are like in California, but Queensland Transport runs at a loss as it is now.

The truth of the matter is holding a license means you passed a license test once, unless you've had to be re-tested for whatever reason. For some people on the road, this license test took place decades ago. How many laws have changed in that time?

The additional costs will be past onto none other than road users, and will in all probability not solve the underlying problem which is inattentive vehicle operators.

"Vehicle" including devices such as cars, bicycles, wheelchairs, etc. (Yes, true fact; here in Queensland, you can be busted for drink-driving if you are wheelchair bound and over the legal alcohol limit. Someone else has to push you until you sober up.)

I've seen it from cyclists, car drivers, truck drivers and pedestrians. Pedestrians can be their own worst enemies at times, and the modern era has brought with it all manner of distractions for all concerned that didn't exist when many of these laws were conceived. Some are more prone to distraction than others.

I myself do ride on the footpath on occasion. In the mornings I commute to work mostly on-road, as at 4AM there's little to no traffic, thus I inconvenience very few. I can be seen for hundreds of meters (probably kilometres) and most of the roads have plenty of room for passing.

In the evenings, I'm on the footpath for parts of the run. Max speed ~30km/hr, slower in narrow spots or where there are blind corners. My preference when encountering pedestrians from behind is to slow down and quietly idle before waiting for a moment to pass safely. Usually a moment arrives, and I make a slow (~7km/hr) careful overtake. If I encounter them coming the other way, I'll generally try to find a spot to pull off the path, then wait for them to pass me. On known blind corners, I ring a bell repeatedly as a warning and slow down.

Usually the courtesy is shown back. I've never had any kind of altercation with anyone so far. I have far more problems with cars.

Regarding arming yourself. Don't even think about swinging lead pipes at people: the moment you do that, you can be charged with assault or worse. Police in most jurisdictions frown on such vigilante action, as do law courts. You might succeed in a civil case for damages, then find your own evidence used against you in criminal proceedings with yourself being on the defence side instead of prosecution.