If both parties agree, then I don't see a problem with a player joining a Major League team straight out of high school. It should be up to the team and the player. If I had been offered a good job right out of high school, I would have been ecstatic.
It would be great to see all players go to college and earn a degree for use as backup if their baseball career doesn't work out, but college isn't for everyone. It's great that high school players can be drafted, which shows what an amazing talent they must have to beat out older, more experienced players.
The goal of the MLB draft is to find the best players that can compete in the game of baseball. Yes, there are plenty of outstanding high school players that might be capable of playing in the MLB. The NBA requires that a player must be at least one year removed from high school, while the NFL requires that a player be three years removed from high school. Playing in a major league sport requires more than just skill; one must have the maturity that is often gained after reaching adulthood. A high school player hasn't had the same experiences to make decisions that someone older has. Therefore, the MLB should create a similar rule that a player must be removed from high school for a period of time, before being eligible for the draft.
Anyone who has the talent to be drafted into professional sports would welcome the opportunity to begin their career as soon as possible, but there is a time for all seasons of life. Today, we are living longer than ever and there is plenty of time to pursue the profession after high school.