A valid point to consider, however not a showstopper by any means.
Where the a/c are receiving numerous distracting practice calls on 121.5 then the transmitting aircraft will, in all probability, be in the vicinity of a ground station. Therefore nothing is lost by turning down the volume of 121.5.
In remote areas you can still do your bit by listening out on 121.5 and if idiots insist on playing games then you can turn the box down until it is quiet again or you can leave it turned down knowing that if a professional wants to talk to you urgently he can do so from his console (ATC) or the cockpit of his armed fighter (QRA); either way, you are not in jeopardy.