But...but... but they'll get million-dollar paydays later!
Oh, wait... that only applies to... what, 5% of them? If that? 1%?
When you decide that signing bonuses are out of control - when you think that Joe Blow should be grateful to sign for $10,000 to "play a kid's game," remember that Joe Blow will probably put in four or five months' service, on the road away from home, for about $1,000/month - for those months he's playing/working only. You wonder why minor leaguers go home in the off-season, and do menial labor/construction/etc.? Because it pays better than playing baseball; the off-season labor makes it possible for them to play "professional" baseball for sub-minimum wages. Most of them will never see a 40-man roster, or the salary that comes with that. And these kids, working for sub-minimum wages, make MLB's profits possible.
When you argue that the draft is "necessary," that a seven-year minor league reserve and a six-year major league reserve are "necessary," to preserve the quality of your entertainment (because that's what we're talking about here), remember that it's these exploited kids who make your quality entertainment possible.
Enjoy the games.