Yes, it is unfair to the woman and unless fully disclosed and accepted upfront with a full understanding of all the ramifications, I would not do it! However...
I was married and had a child before realizing, accepting and dealing with being gay. I would have never done it "for the experience" but I'm very thankful for it. I know for me, and many guys I've talked to who were married and had kids before dealing with their sexuality, I have a different perspective on commitment, relationships and unconditional love (for child) then most gay men.
Certainly when you are married, you are more likely to deal with your relationship issues in a healthy, constructive way for the sake of the marriage and kids. (Either that or you become pretty miserable.) So you develop skill sets that many gay men, without long term relationship experience, simply lack.
Further, a relationship with a woman teaches you to develop the emotional part of your relationship in a deeper way. Women simply are more emotional by nature and to be a good husband, you have to learn how to nurture and develop that connection.
You don't have to get married to a woman to have deeper, more meaningful relationships, but it sure is good training. Not to mention, having kids, teaches you all sorts of things about love and commitment and patience that is hard to duplicate.