Do a search on the topic and you will see that:
Most people find the practice to be selfish, unneccessary and self-indulgent behavior, especially with certain ADR's being increasingly difficult to obtain and if, for example, a large number of people made 5 ADR's for every one they would actually end up using, the system would be clogged and overwhelmed with no-shows.
Some will defend the practice, basically saying, there is no written rule saying that it is against Disney policy and that it is too difficult to know which park they will be in on which day.
People have made multiples with no problem, however I have seen several threads where people were angry because Disney *did* cancel multiple ADR's when they noticed a pattern of abuse in the system. Someone also received a call from Disney asking which one they wanted and which one they didn't (they had 2 ADR's at the same restaurant) It is impractical for Disney to spend the time and money needed to double check every person's ADR's. However, if they do notice it, they have the authority to cancel all of them, and have in a few cases exercised that right.
Morally, I think it's inconsiderate. Factually, I think it is risky, because there is a chance any or all of them could be cancelled.
My personal opinion is that a good way to cut down on this practice would be releasing park hours before ADR eligibility, not after. Until (or IF, I should say!) that ever happens, the best thing to do is to make a plan, make your ADR's and then after park hours come out, call WDW Dining and see if you can switch some things around, always making sure to cancel your unneccessary ADR's.