We have already had this discussion politically, and businesses must make reasonable accommodations for those people that require them. Furthermore, businesses must serve black customers and white customers as equals. And if they bake cakes for straights, they can't refuse to do so for gays. If you want to discriminate, you have to operate as a private club business, and serve only members. That's our "out" for those kinds of businesses. If you want to do business with anyone who walks in off the street, you have to do business with everyone who walks in off the street.

And yes, amusement park rides are discriminatory, but sometimes no reasonable accommodations are possible. The design constraints mean the passenger dimensions have to fall within a certain range, or the physics math doesn't work out. It would certainly be possible to have multiple types of passenger vehicles and restraints, but it also complicates the operations, because you then have to sort passengers by size before seating them. The scope of reasonableness is subjective.

In the case of airline seating, the reasonable accommodation for ranges in height would be to reserve some seats with more legroom for tall people, and some seats with less legroom and lower seat height for short people. Height is normally distributed, so the tradeoff would tend to work out on average. But that would interfere with airlines' fare categories and gratuitous seat upgrade fees.