When I play, I'm usually the first guy to an objective, I revive players when I can, and i've never kicked someone from my lobby. Yet still, 30% of the people I've played with said I was "unsporting". What they really meant to click was "I'm butt-hurt over being outscored in a co-op game".
Don't let it bother you. The rating really means nothing. Play in whatever style you enjoy.
Thx 
I belong to this old kind of gamers who played Sonic, Mortal Kombat 1st of its name, Mario Kart, Alex Kid... on Mega Drive, Master System en Super Nintendo (I even sometimes watch videos of retrogaming on youtube... And I can live with it
).
Even if I've had an XBOX 360 for nearly 5 years, this reputation thing is quite weird to me. My "fear" was that these 66 % of bad reputation would have put me aside on the MP, meaning that the money I spent for my 3 months live would have been thrown in the bin.
I know this thread may look naive to other members, but I really thought that the most part of the gamers community played for fun (as I do), rather than for bullying those who outscore them (I've got 5855 challenge points, 1884 N7 level, but I sometimes get outscored by shorttimers with 125 points and 50 N7, and it does not bother me at all).