Theoretically, our shoulder joints are made to "withstand" a certain amount of weight as well as our knees and hips. If we exert extra weight consistent on our elbows/shoulders, then shouldn't they wear out faster too?
And just what would that weight be, might I ask???? Honestly, and this is just me speaking, I don't think 70-80 lbs is all that heavy and that it correlates exactly to that analogy. Now you boys shooting bows over 100 lbs.....hmmmmm....that might be a different story. But again....what [is] too heavy?
To make blanket generalizations that shooting heavy(?) weight bows is going to cause shoulder problems for everyone down the road is just plain silly and shortsighted. I'm sure as heck not going to depend on someone else to tell me what I can and cannot do. Way too many nay sayers in this world!
Again....I think it all has to do with form. Learn to shoot a bow correctly and you should have no problems, regardless of the weight.....within reason, of course.
The main thing is that you're having fun. Some of us just enjoy the feel of heavier weights. Nothing neanderthal, macho, adolescent or nuckle dragging about it.
Brett