That's a fair point and a grey area, I have my own views but will look into it further as I suggest you do and come to your own conclusion.
For arguments sake, as you have noticed a decline in the songbird population at your feeder an idea would be to change the feeding method for the types of bird your trying to attract. A bird table will attract maggies and pigeons, as will scattering food all over the floor.
Different feeding methods and foods attract different birds.
Location of the feeder? From the list of visiting species you say and in abundant numbers are you on a flight path or