I have been riding a hybrid for y'ars and y'ars. In some ways, hybrids are looked down on more than mountain bikes. People will assume you're out getting some hard miles in to build endurance.
THe knobby tires add a lot of friction, so you might consider putting the Buick tires on it.
I prefer riding a slower bike 'cause I like POWER more than speed. It also means that I'm going the speed of the non-uptight people and still getting a workout. (Or, it's an excuse. Of course I'm not as fast as they are - it's my bike :-))
I've always gotten some comments that made me roll my eyes ("is your road bike in the shop?" "Pretty good for sneakers!" "You're doing well for a..." ) but most of those folks say that as they blow by at 27 mph and I wave & smile.
Riding like you know that yes, you're not going to go as fast because of your tires (not so much the weight) makes you a 'real rider' not somebody who got a mountain bike because they didn't know better (it's all in the attitude!) Anybody who laughs ... well, ya know, some people just have to feel bigger than *somebody.* If it makes their day, fine. You're OUT THERE RIDING. Therefore you are ONE OF US.