There is nothing wrong with expressing one's concerns. Problems arise when governments allow the concerns of NIMBYs to override the greater social good, allow NIMBYs to stall the decision making process, or fail to cerify the legitimacy of the claims being made.

In a case like this, yes it is NIMBYism. On the other hand, having high frequency flights over an existing residential are, for the primary benefit of one party (i.e. Amazon) would seem to support the groundings.