Is the entire concept of having a draft even legal? Shouldn't a player have the right to sign with whatever team he wants (provided they want him), instead of having his employer dictated to him by the league?
An interesting question I've thought about on occasion. As a practical matter, since the NBA went to just two rounds and the NFL cut way back on the number of rounds they have, players drafted are very likely to make the teams they are drafted by and undrafted players are free to pick teams and situations that they view as most beneficial to them.
Professional sports also enjoy some protections from the applications of anti-trust laws, but those laws really can't be used to prevent someone from making a living if they have the ability to compete at that level.