Some very good points here. When I was in my early teens I would have agreed that culling was not so essential. I had a lot to learn, and that is just part of gaining experience as dave mentioned in the above post. You do what you feel is right at the time and learn from it.
If we look at the word "cull"; To some it does mean to dispose of, but for many others it means to remove from the breeding group. It may become a layer for egg sales, given to a person who wants a laying hen, or it may end up on the table.
Any way you look at it, breeding obviously weak chicks will cause future problems. I learned the hard way in my late teens. I had a chick that started out much slower than the rest, but grew into a gorgeous rooster in the end. I used him one season in my breeding project and ended up spending the next 4 years undoing the damage I had done to the line. I learned my lesson the hard way and now automatically move weak appearing chicks to another brooder. They will NEVER end up in my breeding pool for any reason. Nor will they be given to anyone who intends to breed chickens. I feel I am doing the chicken community a great disservice by passing on any less than thrifty birds to anyone who intends to breed for any reason. Years of work trying to improve a breed can be undone in a flash, by making a simple error in judgement as I have learned the hard way. Passing on a less than thrifty bird to any beginner is just setting them up for failure and likely to turn them off from chickens.
Many may say this attitude and need for selection only applies to serious breeders, but the same holds true for the backyard hobbyist. Hatching from a hen that is a poor layer, will produce more chicks with the same characteristic, that only gets worse with each generation.
Just my two cents and view on this.