Look, every action depends on the intention of the heart, if a guy walks up to you and asks your number with good intentions then theres nothing wrong with giving it to him, especially if he met you at an event where he knows he wont see you again.
then again there are plenty of situations where a guy courted a woman in a church "holy" setting over a period of time and married the girl only for her to find out what a slimeball he is...for example: a friend of mine was dating this guy a few years back, he was the most spiritual guy you can get, he preached fantastically, always had a word of encouragement for everyone, was involved in ministry, etc, they eventually got married and two years into their marriage she fell ill and went to the doctor. The doctor told her it was a STD, not HIV but a curable disease. She wondered where it came from and the Doc told her to ask her husband, that night she asked her husband and he immediately confessed that he has been sleeping with prostitutes since before they got married until that very day. What hurt her the most was that she said that there was absolutely no indication that he was into those things, he was a loving husband and took care of all her needs...she eventually divorced him coz he made another woman pregnant.
So it still comes down to if you have found someone you can rely on to have a good marriage, not really the circumstances under which you have met the person (well there is dodgy situations).