STARTING NEW LEAGUE NEED WEIGHT RULE SUGGESTIONS

I have been involved coaching and the administration of age/weight football for over 10 years with over 2,500 players per season. I have started and coached an unlimited weight program for 6th-8th grade players for the past 5 years. Each type of program is essential in allowing all kids to learn, develope and play the greatest game ever. I commend the thousands of coaches out there who give freely of their time to these players. I have a question though that I hope someone can give me an educated answer to. Why would any league put weight restrictions on backs and ends and allow all other position players to weigh much more or even be of unlimited weight? If these types of rules are for the "safety of the players", why are only lighter kids allowed to be hit, tackled, blocked, knock down, etc. by kids who can weigh much more? If "safety" is such an issue, maybe some physicist should explain what happens when two bodies collide and one weighs 120lbs and the other weighs 160lbs. Is there a change in the collision dependent upon who has the ball?
I think all the Youth Football Gurus out there need to realize that this is 1999 and get off the "righteous safety" issue and let kids PLAY FOOTBALL! By the way, I mean all kids of every shape, size, weight, color and form. Not just the little kids. (150lbs. and under.)