The relevant thread convoluted...
I am Poly because:
I found a relationship that makes me feel better than anything else ever has.
I realized I don't care if he's with someone else, so long as my needs are met.
I realized the sort of person who is good at one relationship is good at many; and his or her being poly is inevitable. I WANT someone who is so awesome that more than one person wants to be with him and commit to him.
I don't want to restrict myself to loving one person.
I don't always have the capability of taking care of my partner, or being with him, and am grateful he has others who can.
In the same way, he can't always be there for me, and I'm glad I have others there for me.
It just makes sense.
I enjoy being able to build on to something that already exists, and not have to start from just me and one person.
I love the honesty and transparency.
Could I be in a healthy, mono relationship? Sure. But it'd be harder, not easier, to be involved with one person. At least for me.
...and yes, I am technically single, and yes, there is plenty that sucks about being single and dating an attached partner with a live-in. I won't bother to list them here, suffice it to say, none of them outweigh the benefits listed above
Love to hear other perspectives!