No problem with players getting as much as possible.
It is well known in negotiating tactics that deadlines allow parties to create leverage. Almost all Boras clients wait until the deadline and that is their right. The issue is not whether the players are greedy but whether or not it is in their best interest to bypass almost one year of pro ball waiting for the deadline to occur. As a secondary issue, I think it does cause some loss of political capital with the fans when a holdout occurs. Not saying that is right either but perception sometimes is reality and holdout players may be given a shorter leesh by the fans when they fail.
IMHO, a player will likely not get all the money they may have gotten otherwise if they sign before the deadline. They may make up for it in the long run however if they get better fan support and possibly quicker development time to the big leagues.