How do you call someone who is religious only because it makes them feel happy?

[Magilla]

. . .

I guess I didn't express myself clearly enough. I referred to people who practice religion out of comfort. I wanted to include polytheistic religions too.

It depends upon how loosely you are using language.
On the proposition: "A god exists" a person may agree, (ie. believe), or they may not.
On the proposition: "More than one god exists" a person may agree, (ie. believe), or they may not.
On those propositions, there is no middle ground, a person believes or they do not.

When in agreement, a person is a theist, ({ believe in a god } = { theist } is a tautology).
When not in agreement, a person is NOT a theist, (that is also a tautology).
When a person is NOT a theist, they are an atheist, (ie. just another tautology).

To be an atheist requires no effort. I read in this thread that some people were apatheists, ie. atheist by virtue of not giving a damn.
On the other hand, a person with a bit of effort can arrive at the atheist position, by some consideration of the evidence and arguments, pro and con.
If a person is unsure whether or not a god exists, they are NOT theists, and so are atheists. These people are agnostic atheists.
Being agnostic is about knowledge. One can be an atheist by virtue of not being convinced by the evidence and arguments, pro and con.
The agnostic has insufficient confidence to say that their level of knowledge confirms a justified belief in a god or gods.

Some other atheists are convinced that the evidence and arguments pro and con, are sufficient for them to to accept that: "No gods exist."
These latter people may be called strong or positive atheists.

So the question you need to be asking Die Atheistin is: "If you asked these people that you know . . . 'Do you truly believe in the existence of any god or gods'?"
then if the answer is: 'YES', it is tautological that they are theists.
If the true answer is: 'NO or I DON'T KNOW FOR SURE", then they must be atheists.

Going to church purely because it makes one feel good, is not an instance of true belief in a god or gods, therefore it indicates atheism.