My argument against the rule being applied to college ball would be that (compared to MLB) there's just not enough talent in the pool for the number of college teams. Implementing that rule in college ball would further the domination of the large$t programs who can $tack a roster, while diminishing the ability of le$$er schools to compete.
I imagine it would also restrict the development of young pitchers. Currently, you can bring in a youngster to face one batter they're well suited for, experience the inner nervousness and crowd awareness of pitching at this level, and develop incrementally as opportunities present.
If their "first opportunity" to pitch at this level requires facing 3 batters instead of just one, well... you just can't do that with a young pitcher in the SEC. It also means fewer pitchers get to pitch in any single game. So the young pitcher's college experience might be to pitch in only a very few non-conference games early in the year, then sit for the rest of the season.
I'm sure there are also some legitimate arguments for the proposal, these are just the first ones that jumped out at me.