you start with it because its the standard issue rifle of the US military. (soon to be M4 carbine). and i think they were going for realism while less fun for you the player (most likely with little knowledge of military weapons) its more realistic. your no longer going to rush someone because they ONLY have a pistol.
if i shot you in the head with a baretta M92F (M9) you will die
if i shot you in the head with a M16A2 (M-16) you will die
if i shot you in the head with a M82 Barrett .50 Caliber sniper rifle you will die and paint the wall behind you.
so while it makes little differnce what you pick. look at it this way. you can use whatever one you think "just looks cool" and not have to worry about it sucking. (and i love the look of the M16A2!)
if i shot you in the head with a baretta M92F (M9) you will die
if i shot you in the head with a M16A2 (M-16) you will die
if i shot you in the head with a M82 Barrett .50 Caliber sniper rifle you will die and paint the wall behind you.
so while it makes little differnce what you pick. look at it this way. you can use whatever one you think "just looks cool" and not have to worry about it sucking. (and i love the look of the M16A2!)