So, you'd swap a 'great idea' 99% of the time to cover 1% of the time that a keeper gets injured? (I made those percentages up but probably not far from reality).
I won't be convinced that it's a bad idea to not have a keeper on the bench until someone (MLG?) can throw up the statistics and/or mathematic probability that it affects results adversely (on average, over the course of a season)