Is it considered unhealthy and even dangerous to not eat any carbohydrates at all?

Yes, it would be: Yes it would be - i don't know how one would extract all carbs from their intake.

No - but why do it?: Carbohydrates are natural foods which contain sugars and starches, both of which your body needs for energy. Your body can make sugar and starch out of protein (meat, dairy, and foods which are not starchy), so you could substitute them, but it is more work. Most people who avoid carbs are tryin to lose weight. There are better ways, cutting portion size for example, than cutting out a whole class

Look up keto diet: The ketogenic diet is all about reducing your carb intake as close to zero as possible. It is very difficult to have a zero carb intake but ketogenic is as close as possible. When you take in zero carbs it is not dangerous to people of good health as long as they stay well hydrated but can cause fatigue and ill feelings or the “keto flu”. I suggest they you read up on the ketogenic diet.

IT is difficult: You can avoid carbohydrates but you would need to relace the vitamins that you miss by not eating vegetables and fruits.