For the ones who don't believe you, they need to go to an amateur tournament. It's not unusual to see fighters 5-10 and over at 141, by 152, you're seeing guys who walk around in the 170s, maybe 180s. Often it seems like the 165s are the biggest kids in the tournament, by height. Just because a guy fights at a light weight doesn't mean he is the same size as untrained people of the same weight. The kid who was a good high school football player at 5-8, 155-60 and is looking for a new sport after graduation, will often box at 132 or 141. The ones who get into boxing and want to fight without cutting weight usually find they are too small if they fight at their "walking around" or "natural" weight and they cut weight themselves if they want to stay in boxing. A kid who played football at 155-60 and wants to fight at that weight will often find himself boxing against kids who are near 6-0 or even taller and who were 185 or so when they got into boxing. The ones who want to box and stay in the sport will usually figure out what weight they want to be and they usually want to be in a class where they will be big.