My answer is... no they aren't fragile, yes you can put them wherever you want but as any bike obviously if you dont give a damm about it for sure you will crack it or something.

You have to be careful just like with any bike but if you used to just toss it like a 200 pounds potato sack in the back of the car, it is more than clear that in that way it will crack sooner or later.

As probe of their durability, you still have the original trek carbon bikes moving around, many of those were manufactured like 20 years ago. The issue is that many people think that carbon is a new material that stores are selling just in the last 2 years and the material has been used for bikes from back in the mid 80's early 90s. Old Ketrels, treks, vitus and other brands are still moving around.

Seen steel tubes dent or craked because the user did not care about the bike, if you dont care about the bike then you will crack, dent or destroy what ever you buy, no matter what the bike is made of.

Good luck.