Drilling for rivets is also dangerous when done incorrectly. You do not want to be riding at full steam when the frame cracks, it's nasty.
High carbon, stainless, and fancy stuff is where you can run into problems. In general you won't see this on car or bike frames, too expensive in bulk.
If it's a newer bike it's probably aluminum which you can usually still weld with impunity. If it was high grade alloy the heat could matter, but as far as I know nobody cares that much about bike frames. Heat treatment, or "seasoning" in the case of some aluminum is expensive.
Source: used to cut up old bikes and weld the frames into crazy chariot contraptions we would tow around
Steel is real, man. It'll bend, not break.
But in seriousness, yeah, I was following very closely behind a fellow who snapped his fork jumping over a bump in the road. I almost went over him. Despite the helmet, he lost memory of the accident. I called an ambulance for him and left my number. He called me the next day asking what had happened.
It was a nice aluminum frame, looked in good condition. Always check carefully for hairline fractures when buying a used aluminum bike.
Amsterdam is a smalll place so having a fluro green bike with a number plate of your name welded to the frame is a good deterrent.