You clearly feel that sexual history is highly correlated to moral character. This is a common position. Its not that you may be wrong (neither position can be proven) but more importantly if that's how you "feel" then you know what kind of woman to exclude from your search. Its great to find a "nice girl" and live happily ever after. Please be careful though to not brand people as immoral simply because their past is different than yours. Its better to simply talk about "compatible" instead of moral. Character judgment like this is a slippery slope.
From my perspective, I do not find a strong correlation between "sexual history" and "morality". I do find a strong correlation between "sexual history" and "sexual 'fitness'". This doesn't make me correct. Its my perspective and I don't project moral character with it.
Bringing up the topic of sexual history with a woman is generally a huge turnoff. When you do so, you are clearly judging her and telling her she must fit some predetermined notion of what you, a man, thinks a woman's place is in the world. It doesn't matter if you actual think you think so. Its what most women hear when you bring up this topic.
Additionally, I have found that many men that feel as you do have internal feelings of sexual inadequacy and/or "control issues" and in turn project these feelings into a moral dilemma on others. My only training on this matter is from living my own life and having to grow out of some of these issues myself. To put is bluntly, this is the common story of the geek who didn't get laid in high school and has evolved a blanket of morality around the reasons why.