Gary T:Yeah, I agree that there are songwriters out there who consistently spew crap, but eventually the Darwinian forces will remove their stuff from the vicinity...unless they have a really good record contract (which explains the Spice Girls, Michael Jackson, Garth Brookes, et al)...
The way I generally determine if a specific self-penned song really sucks is if after I've performed it at least a few times to the same basic audience (on different evenings, of course!),I still get NO reaction...as a general rule, the audiences are very good about letting S/S's know, usually in no uncertain terms!
The will of the people must be respected!