I had never sat through this entire movie. The last time I attempted (or rather, my family attempted) I fell asleep halfway through it. This time I was wide awake through the whole thing and enjoyed all the music, dancing, and great story.
I was kind of wondering where the movie was going with Sky Masterson's initial outlook on women as "toys." He harped on Nathan Detroit and his 14-year relationship with a single woman and boasted that he could get any woman he wanted. Nathan takes him up on his bet, desperate for some dough to fund his floating crap game and selects a woman from a religious group who preaches against such gamblers as Sky and Nathan.
Through a series of wonderful musical scenes, including Marlon Brando singing and dancing, you see a very realistic change of heart for his character, Sky. He sees that women really are more than just toys and feels something stronger than he's ever felt before. In today's movies he would have made that realization and still slept with the girl claiming he found "true love"; but he doesn't. While in Cuba, he realizes the drunken state he's lured his victim into and respectfully flies her home in the middle of the night.
The only possible qualm that could exist on the morality of the movie is the fact that gambling was shown as "saving" Sky's and Sarah's relationship; but it allowed Sky to keep his word (marker) which was another strong positive in the movie and outweighs the sin of gambling. Also, the idea of marriage was made light of throughout the film in the depiction of the relationship between Nathan and Adelaide. I believe this depiction actually helped strengthen the argument that marriage is essential between a man and a woman, Nathan just needed a stronger person to show him the importance of it, though there's no implication that he fully appreciated the end situation.