maybe someone may accidentally turn the camera on without the card or something
When you turn on the camera without card, it loads the original firmware. This procedure (starting without card) is the first thing one should do if the camera doesn't boot (see the Troubleshooting section on the main download page), so warning others not to do this, doesn't make any sense to me.
"skipping loading modules"
This one appears after a bad shutdown while you were running ML. That is, after removing the ML card, the camera was not fully turned off, and when you started it without card, it was actually running from the previous (ML) session. I've seen Canon firmware canceling a shutdown in the past (if you power the camera back on before the shutdown completes, or if something goes wrong with DryOS). So, yeah, I can see a way for this to happen after a crash.
If the camera doesn't boot, remove the battery and retry. The power button doesn't actually cut the power; it's just a soft button, so it's not going to bypass a software lockup. Same for the battery/card door.
I think one shouldn´t. It´s better to uninstall ml if not using it or removing the card etc.
Sorry, but that's nonsense. Using a formatted card, or removing the card, are preferred ways to start the camera without ML (see FAQ and install guide). One shouldn't have to run the installation procedure back and forth.