My duty as a literary agent is to represent my clients to the best of my ability, and by and large this entails selling the rights to their works.
I do not believe that reading queries and providing feedback is part of my job description (and since I'm my own boss, I'm the final arbitrator of this). I've provided query guidance in the past on this blog, but only as a means so that I get better queries, and I read queries for a single purpose- to get clients in order to sell the rights to their works.
But no matter how irritated I might get over the really, really bad ones (see my post from last Tuesday), I will still respond to every query sent to me through my website, and if rejecting will continue to convey my "this is not for me" response. I do this for three reasons: 1) so that writers will continue to be encouraged to query me in the future; 2) in the hope that writers will treat me with the same professionalism that I treat them; and 3) good karma.
I hope this reassures any aspiring writer out there who thought I might release a tirade of abuse upon them when receiving their query.