This response is far from comprehensive, but I'll hit some key points:
-I'm not saying a "split" is necessarily bad. I'm saying full body workouts are good (and of the cases I've seen are better than most splits).
-A full body workout, to many people, means doing the exact same routine every time. That's not always the case. Take the ever popular "madcow'd" Bill Starr 5x5. The monday/friday workouts are composed of different exercises than the weds. workout, but they both hit all the muscle groups.
-Unless the whole program is isolation exercises you're gonna have carryover to the rmuscle groups anyway. I.E. A "chest day" that includes any pressing will stress almost the entire upper body. Deads hit just about everything. You're fooling yourself if you think other parts aren't getting trained over the course of the split. So take the next logical step and train the whole body intentionally.
-A common argument for splits is that "muscles need 48 hours (or whatever) to rest so they can grow". THis argument is unfounded. It takes upwards of a month for a muscle to fully recover from training. You don't WANT full revovery - you want adaptation as a result of fatigue. Fatigue is systemic. The body needs to be fatigued for stimulus to occur, which is why workouts need to be progressively more challenging by increasing any/all of the three main variables in programming: intensity (% of 1rm), volume (# of working reps) and frequency (how often the work is performed).
The reason I got my panties in a bunch over this was Herpecin saying anything's better than full body workouts for sports. Well just about every S&C program I've seen uses full body training. He spouted BS as gospel, which irks me.