Triggerman saidAs an atheist, why should I care what a bunch of believers in the Supernatural believe in? Because all religious beliefs are beliefs in the Supernatural. Greater than nature. Thus, Super...Natural. Like UFO's and Loch Ness Monster
If you really don't understand why you should care what others believe, I shall explain.
What people believe influences their behavior towards other people. It is unclear to me why that is not obvious especially considering how some politicians have been behaving for the last several years and what laws they are attempting to enact. Moreover, if you understood that in which you do not believe (and it is possible to understand what one does not believe), you could at least use that understanding to oppose more effectively some of the silly and oppressive legislation that fundamentalists are attempting to enact.
When Jesus was asked which is the most important command, the second half of his response was, "Thou shalt love thy neighbor as thyself.". Via the parable of the Good Samaritan, He greatly expanded the definition of "neighbor" and made it clear that love was not mere sentiment, but rather, required helping and caring for one's neighbor.
If you understood that, you would quite clearly see that attempting to repeal Social Security, attempting to repeal legislation which enables many people to have adequate medical care, etc. etc., are contrary to the very principals which the reactionary and hateful fundamentalists are supposed to support. Pointing that out to them would tend to undermine their effectiveness in enacting legislation which is contrary to the social justice that Christianity is supposed to support.
The above should clearly explain why you should care what others believe.