IMHO, I think that the touching issue is a personal one. I know people who let others handle the cards, some that only allow others to handle them to cut/shuffle for a reading, and others who do not let anyone touch them under any circumstances. As for me, I prefer that no one touch them exept to do their reading. The idea is that when someone handles your cards, they leave a bit of their aura and energy on them. It helps with the accuracy of the reading. This includes any negativity or malice that the person may be feeling at that time. To remove any bad vibes, I always reshuffle the cards after I read, before I put them away. As I do this, I visualize the cards being cleansed of all energy except my own. The more you handle your cards, the more "yours" they become. There are a very select few people that I will allow to borrow my cards for a reading on either me or them, but these are people I know and trust not to leave anything "icky" on my cards. The only other time I have ever let anyone hold a card is when I had the Ace of Cups tattooed on my ankle. He had to hold it to reproduce it. Because I did not know him that well, I did a cleansing ritual on my deck when I got home.
I know this is pretty long, but I hope it helped.