Not fragile in the sense of likely to break in half, but fragile in the sense of not optimized for utility riding and requiring much more maintenance and general tinkering per mile than a typical car, while delivering less reliability. Keep in mind that the whole point of a hybrid is that it's not optimized for anything. That's both the good part and the bad part.

Problems that I have experienced: Derailleur gears that get fouled by road sand and salt during the winter and require adjustment. Tires with the flat resistance of Formula One rubber. No fenders. Brakes that require a new set of pads every month or so and wear out the rims every winter. An exposed chain drive that eats clothing and catches spray, salt and road crud. In summary, a better gear range than the British 3 speeds of the 1960s, but inferior in all other respects.

Most of these problems are only a factor during daily use and particularly in winter cycling. If you don't use your bike like this, a hybrid is fine. My Specialized Crossroads drove me nuts when it was my primary daily transportation (I compare the experience to using a violin to drive nails), but is a joy to ride on weekends and as my emergency backup bike. It also cost less than a third what my primary bike did.

Paul