Dear all, please be gentle with these people instead of condemning them. I grew up in a family like that and understand what they're coming from. They don't mean to judge you, most of the time, they're just afraid and may really be concerned for you, because they truly believe that evil forces use occult means to infiltrate in people's lives. I know it sounds naive, but then again, believing that tarot cards do reveal a truth, may sound just as naive. Really, most christians are just idealists who want to work towards a better world, just like most people here, even if they approach it differently.
Also, please be careful with generalising 'christian'. There are lots of types of christianity. Some very fundamentalist, some very open and loving and liberating. American christians are very different from European christians, etc etc.
But yes, it's very, very frustrating to get that reaction. It annoys me too, every time it happens. That's why I don't tell strangers about being interested in tarot. (Well, here in Europe most people won't object for religious reasons, but because they think it's a silly superstition that no intelligent person can take seriously.) There are even some friends I can't tell, not because they would judge me, but because they would be genuinely concerned and I don't want to upset them for nothing. I guess people's negative reaction is just something I try to anticipate and circumvent. Whenever I do get that reaction, I just reply that I think a fear-based approach to life is even more dangerous, because it tends to lead to black-and-white thinking and demonising the opposite side. As a general remark, so they can't feel attacked. That's all. And then I go about my business.