It doesn't seem like many give Miroku's perverse nature a second thought. They think "Oh, well, he's just really perverted." Granted, he does hit on more women than any other male character in the series but he's also nineteen years old. He's really not that much more perverse than other guys his own age... he just happens to be more forward and confident, and as the title of this site implies, he's void of restraint.
Both Kagome and Sango, when first meeting Miroku, have distanced themselves from him by calling him "Miroku-sama." They really don't trust him because they're more familiar with Miroku's delinquent behaviour. When Miroku decides to do some good for villagers where beautiful women may be involved, both Sango and Kagome see right through his behaviour. Regular village women who have never seen Miroku before, however, tend to not really know about Miroku's more devious personality and usually view him as a rather charming young man. The fact that Miroku is a Buddhist priest aids in his... er, plans for skirt chasing. ^^; How many people are suspicious of a man who is supposed to be holy?
It seems as if the only women Miroku doesn't like are the old or ugly ones... which is kind of superficial on his part but understandable. It's pretty obvious why Miroku goes after the cute girls... and he certainly doesn't seem to be bothered by whether or not they're human or youkai. If they have a cute appearance, Miroku's interested. ;p He constantly approaches beautiful women, asking them if they would do the honour of bearing his child. Which brings us to the next point...
The reason why Miroku's such a pervert is partially because he's just acting like a normal guy his age but also because of the hardship that he has to endure. He spends every day on Naraku's trail, with the intention of killing the one who gave his family the curse of the kazana. If he doesn't kill Naraku, his family will have been eradicated... and he considers it his duty to find a woman to have a child with, so that if he fails, his child will have a chance of succeeding in getting rid of the curse. Until he can kill Naraku, Miroku's life span is rather short and this makes him rather desperate to find someone suitable to have a child with.
I think we all know that he's found that certain someone. ^_- But being the pervert that he is, Miroku really doesn't stop. If he already has captured Sango's heart, why bother going on with asking every woman he sees if they'll bear his child? It could be a bad habit that he has yet to break or maybe it's just a part of his personality that will never go away (who can't see Miroku and Sango married, with children, and Miroku still asking women to bear his child? XD). There's also a chance that Miroku might think that the more children he has, the better chance of defeating Naraku there is... either way, it's all a part of Miroku's personality and behaviour that his fans have come to adore. Miroku not being perverted just wouldn't be Miroku!