Who to stand by....

I have always been a person to hold on to the illusion that everyone and I mean everyone has good intentions. With that I wonder who or what do I hold true to? I get a horrible feeling every time some one is put down and once again who do I stand by? I know that my family is one that I defend without batting an eye, but when it comes to friends when do I stand up or let things go? I live with wonderful people that I do not always see eye to eye, it is under our roof that I hear hurtfull words about people I care about. Is it consider betrayl to my roommates to not side with them? Yes I am entitled to my opinions, but to honestly say I disagree and don't ever bring it up again, is that an OK answer? Questions I try to answer daily and yet still have no clue to who I stand by?