I have been on M:S a few times and each of the times it felt like it was difficult to breathe. The reason for this is the G-forces pressing in on your chest. At times it can feel like a 200 pound football player is sitting on your chest.
I found that if I reminded myself to breathe during the launch sequence and take deep breaths, I was able to enjoy the ride.
I think that the reason that people have problems with the ride is out of ignorance. There are a plethora of warning signs about the intensity of the ride, but people are disregarding them thinking that nothing in an "amusement park" could hurt them. :brick:
I'm a father, and I don't care if my four year old is big enough to ride. I would not let my daughter on a ride that I hadn't scoped out first. This is why people get hurt, or, sadly in the case of M:S, killed.