I started riding in AZ, which does not allow splitting.

I now live in CA, which does.

The actual justification for it is valid, but mostly outdated:

Older and less powerful motorcycles often have air-cooled engines, and if you sit idling in them in e.g. a traffic jam, they will absolutely overheat and die (at best).

Newer and more powerful bikes are liquid-cooled, and do not have this issue (though the driver overheating is another very real issue).

My personal take is that most riders who use bikes to commute are too reckless, and lane split at speed rather than doing so more safely.

25 mph or below, in fully-stopped traffic, is relatively safe. Ditto for <=35 in a 10-20 mph flow. Each of those gives you a relative stopping distance of about 50 feet, which is 3 or fewer car lengths, which is easy to account for.

60 in a 25mph flow OTOH isn't lane splitting, it's just weaving through traffic recklessly, hoping to God that no one in the next 20 cars lengths merges or drifts at all.

It's actually safer-ish. First: terms. Filtering is good, involves moving slowly through stopped traffic between the cars, usually under 20mph differential.

Splitting is less good, that involves weaving between cars at speed and is actually dangerous.

Some of the worst accidents are rear endings where drivers (not paying attention) just run you over while stopped in traffic.

This is offset by accidents where people do the stuff you're worried about but when it's practiced correctly that's not as big of a risk and generally leads to less catastrophic accidents than rear endings.

It's also just kinda dumb to force a class of vehicle that can get out of traffic jams to instead sit in them