Yeah they can be dangerous for sure. Both cycles and quads have their pitfalls. Before I ever had a motor-bike, I had a tiny Suzuki LT50 quad.
They weren't sold anywhere at that time because of children flipping them and being badly hurt by their weight. It even had a "leash" with a plug that would kill the fuel pump I assume, but it was for if the child rode too far ahead of the adult.
I rode that thing forever, and even cracked the chassis which my father ended up welding.

My first bike was a brand-new Yamaha PW-80 with an automatic clutch, and 3 or 4 speeds. Obviously with 2 wheels there's more of a chance of losing balance/traction, and I always worried about being burned on the leg by the engine but that never happened.

With either style, terrain is a big factor. I live in Maryland, and we'd ride in a lot of different environments. In the woods there would always be mud to contend with, and a lot of steep climbs that were perilous on either type of bike.

I watched my father and his friend try to summit a 70+ foot hill with a 60-70 degree incline on their Kawasaki Mojave quads. Both of them ended up losing grip well over half way up, but my father's bike actually flipped backwards and came all the way back down without him on it. He ended up scratching his eye on a Holley tree.

Quads are great in the snow though, and that can't be said for dirtbikes.