Kinda confused... Where do I start?

[aburwell89]

By gaining weight you are sacrificing a huge natural advantage in boxing competition; in terms of height and reach.

I'm sorry, but I don't know what you mean?

If you fight at 140lbs, thats light Welterweight. The average Light welter is 5' 6''

You will have a huge height advantage over your opposition.
Your arms will also be far longer allowing you to pick him off with your reach.

If you go up in weight, you'll fight taller guys, that can hit harder and like to hit.

But I'm a rail at 140, I can't even concieve putting on enough mass to do any sort of damage to anyone competing at that weight. I mean, maybe I'm just a dumb kid and don't know what I'm talking about, but I just don't think it's manageable given my frame.