See clip from Attorney Rajiv S. Khanna's conference call video that addresses this question.
It will be wrong if you entered USA for a visit visa and had a preconceived intention of getting married. I think that would be considered as a fraud by the government. On the other hand, you entered USA wanting to visit and fell head over heels in love with somebody, I think in a case like this we can definitely go and do a green card if you can demonstrate that you had no preconceived intention then I think you are ok.
My advice to people is don’t get married till you apply for a K-1 (fiancé visa) which would be a smart thing to do in a situation like this. It takes a few months or maybe more than a year.