Before I had DC I would have said go for it, who needs a man, single parents do a great job all the time.... etc etc.
Within a few weeks of having DS1 it became clear that having a family is flippin' hard, wonderful but oh so hard. It's not just all the practical stuff that needs doing, but the emotional stress of having little ones (and later not so little ones) completely dependent on you. I have a wonderful supportive partner and it's hard, I can't begin to imagine how hard it is to do it on your own, to be on your own when 6mo has a sky high temp or 13yo has been caught shoplifting...
I know there are loads of fantastic single mums nearly killing themselves to be everything that a father would be to their DC, but I also know that DH and I are completely different to each other in the way that we deal with our DC. We're consistent and work as a team, but we each bring something different to their upbringing. Mostly though we support each other with all the difficult decisions.
That said I also think that "it takes a village to raise a child" is true and Grandparents, friends of all ages, sports coaches, elderly and teenage neighbours, church and scout leaders etc are vital, so if you have a good network of those people around you, you might be better off that couples doing it all on their own.
I echo what carrots said, lots of parent end up single and work hard to do a good job, but to set out doing that deliberately, especially when you have no real idea of what it is to be a parent or how that will affect you physically and emotionally is an altogether different matter.