There's a difference between cheating, and having multiple partners. Cheating requires an active engagement with your significant other in which you both agree to be monogamous, but one of the parties engages in sexual acts outside of this agreement. Taking word for word from this quote, he's saying he's slept with other women while his girlfriend was expecting a monogamous relationship.
In other posts Magisleeper has said he is open about having multiple partners outside his relationship, and his significant other is as well. This is not cheating, if it's previously agreed upon as being alright.
So really, I think everyone attacking him is confused about his meaning. I had to read through the thread to get his point, which I agree with. Sex with other partners is fine if you and your significant other agree to it beforehand.
Cheating, as defined by one engaging in sexual activities with another partner who is not their significant other without their significant other agreeing to it beforehand however, is not fine. I'm perfectly happy in a monogamous relationship, and cannot forsee myself cheating on my soon-to-be-wife. Not for some religious ideology (I'm an atheist), but simply because that's how I choose to love, and we agree on this point. If one of us did not, then the relationship wouldn't exist today.
I've been cheated on, while I was struggling to hold on to a crumbling relationship. 8 months later I found out she was pregnant, and 3 months later she had the baby (this puts her at 11 months after our relationship ended.) For two months I was on edge, worrying that I had a baby on the way with a woman I wanted nothing to do with anymore. Luckily, after the 9th and 10th months came and went, I knew I was in the clear.
I'm a firm believer in to each their own, so long as you do not harm someone else, physically or emotionally, in the process.