Question

Are archaea dangerous?

Answer 1

Well, some are...

Explanation:

We cannot say that all organisms of a certain domain are dangerous to us. However, some archaea can cause disease in animals and humans alike.

There is one type of archaea that is found to cause disease in humans, you can read about it here:

https://socratic.org/questions/how-can-archaea-be-harmful

Answer 2

They can and have caused explosions...

Explanation:

The first archaea identified were methanogens, which cause cows to produce large quantities of methane. Apart from the potentially harmful effects of methane as a greenhouse gas, it has been known to collect in sufficient quantities in cow sheds to cause explosions.