It depends on the circumstances and factors such as whether you work, how many children you have etc. But in the majority of cases I think it is easier, yes.
If you have a genuine partnership with a person who respects you, supports you and is committed to playing his part in the family and the marriage, being married is easier.
I strongly suspect that that accounts for a very small proportion of marriages. In the vast majority of marriages I know of, even the supposedly "progressive" ones where the woman has her own career and the man prides himself on "doing his bit", the women are still doing the lion's share of the childcare, domestic work and admin (unless they are rich enough to be able to outsource everything). I don't see men bringing a great deal to the table other than money.
As others have said, the transition out of a marriage can be traumatic and difficult and will involve some financial hit. But I think in most cases the autonomy and control you get back, the ability to plan your life and freedom from the constant biting resentment of not having to do everything will be worth it.
I personally found being a single parent a million times easier than being married to someone who did sweet FA other than cooking, who went to the pub after work every night and refused to get out of bed at weekends and who gave me minimal financial support. I was working with a reasonably good salary and I had one kid so it was almost a no brainer. If I'd had four kids and lived on benefits it would have been harder.
I still think though, nine times out of ten if you've got to the point of feeling really resentful you're better off on your own.