Some people want to shoot as much as possible. Others only want to take that one, perfect, shot. Most of us occupy positions in between, and adjust them according to our circumstances, to the challenges we set ourselves, and the etiquette of the day.
All things being equal, if you don't want to be caught out with your rifle empty, then a detachable magazine -high-capacity or not- and a couple of spares is as practical a solution as any.
I don't think there's any virtue in not shooting just because you haven't been able to put rounds in the rifle in time.
On the other hand, where there is a written or unwritten rule regarding capacity, then that limitation becomes an integral part of the sport.