In the case of a cheap 16awg cord, yes you have created a dangerous situation, but it is not one that is considered part of a larger structure in terms of code. This is the electrical equivalent of spraying gasoline around at the gas station and acting surprised when it turns out poorly for everyone.

> however that's something that I wouldn't do, so its not really my issue

Electrical code is designed so that even an incompetent operator cannot produce a dangerous situation inside a building's electrical system. OSHA, USCSB, et. al. would be the first to tell you that relying on a specific individual to interlock a dangerous situation can result in extremely adverse outcomes.

>There is nothing stopping me from getting an adapter to plug a space heater with a cheap 16awg cord with an adapter into a 30a outlet

That would be against code.

There's nothing stopping you from running bare wire through your walls.

There's nothing stopping you from not bothering to ground any outlets.

There's nothing stopping you from using 14AWG romex on a 50 amp breaker.

Etc., Etc.

All of that is against code, and I've personally seen all of that in the wild at people's homes, offices, etc.

If you wanted to do things the #rightway, you'd most likely need a subpanel for the UPS to feed.