Never had a crash from that. When the GameObject is destroyed, the coroutine is gone. If you're using a coroutine to manage something outside the scope of the GameObject itself, that's a problem with your own design, not the coroutine itself.

It'd be like complaining about arrays being bad because if you pass a pointer to another object, nuke the original array, then try to access the data, it'll cause an error. That's kind of... your own fault? Got to manage your data better.

Unity's own developers use them for engine code. To claim it's just something for noobs is a bit of an interesting take, since, well, the engine developers are clearly using them and I doubt they're Unity noobs. They made the engine.