Not even... most Atheist don't care what people believe in, they just don't like it when religious people try to force their own personally views onto other people.
Also, I'm not sure what religion you believe in. But, the Bible states that you must kill people that don't believe in the same religion as you. So, if you're a Christian, that post is very hypocritical.
Because there is very little evidence that supports the existence of a 'Supreme Being'. That would be the main reason imo. Another, is because religion was firstly used as a means to explain the explainable; but then was used for gain, to control the people, to 'scare' people into submission to the church and as a means to create wealth.