Scrap all religion?

My nanny (grandmother, not child carer) believes in the christian god. She lost her sister when she was young and so clings to the hope that they'll be reunited in heaven.

I don't believe in her god - I am atheist about all gods including hers. We have discussions, during which I am constantly aware of her reason for worship and belief (although admittedly some days I may be in a funny mood and not have the patience for such considerations).

I take the view that if it makes her happy then what's the problem? Also by the time that she does die it won't matter what she believed during her life because she'll be no more and none the wiser. 

But there are people out there who do cause suffering to others because of their beliefs. For the sake of the harmers does this mean that all religion should be scrapped? How can you permit some people to believe but deny it to others, when belief is the same across the board?