What weapons in Modern Warfare 2 are you allowed to use?

In my opinion most people that say "this gun is for noobs that gun is for noobs" and so forth are in just saying it as they cannot use them i mean i use the SCAR quite alot and im always in the top 6 personally i love the barreta i just think that it is just stupid and wierd that people that can not use specific weapons in cod 6 call everyone noobs that can use them and for this i sympathise with you as it just (as i said earlier) stupid and wierd.