This is the best way I can summarize how I see things:
being in a great relationship>>>>>>>>being single>>being in an descent/"average" relationship>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>being in a bad relationship
Being in a really good relationship has some really good upsides to it. For the somewhat small percentage of people who can keep a good relationship going on for a long time, congrats to you.
To me, the freedom of being single outweighs the baggage of a relationship that is anything less than a really good one. Of course, it is hard to quantify exactly what makes a awesome/great/good/descent/average relationship. It just comes down to how you feel in your heart.
But being in a bad relationship, oh man, let's just say I could have filled the screen with those > signs, but I didn't want to be a jerk about it.
I believe that the greatest problem lies in the fact that most relationships start out high on the good side of the scale, but by the time they become bad, if they do, leaving the relationship may be difficult, and the damage done can be extensive. My:2 cents: