This has been discussed a lot of times on AT, quite the popular subject...
A lot of us believe that the cards are a tool. The images are powerful and spiritual, but the cards are a tool that channel our intuition and inner feelings etc. Cards don't get mad, sad or jealous, just like your favourite book wouldn't be mad and change its' content because you buy other books and enjoy them too. I'm one of the people that have this view. I'm comfortable with seeing it like this and since I started using the tarot cards (in 2004 or 2005) I've never felt this is wrong in any way.
But others on AT do believe that the cards have a personality, soul and such. They believe their decks get mad, sad, etc. I have a hard time understanding this view - like someone said, does your car get mad if you let someone else drive it? But sure, if someone truly believes that their deck has a spirit, personality and a mood, yeah that's their cup of tea and I'm not gonna work my butt off to prove them wrong.
It seems like a lot of books and websites still promote that you have to treat your deck a certain way (use a wooden box, cleanse them with certain rituals and bla bla), and I think that makes people believe the cards are their own creature, without actually trying to figure out themselves what they believe when it comes to this matter.