Could you be
I help your society live, but I can bring it to its knees
Life requires the energy/ heat from the sun. The sun can bring you to your knees in solar storms, explained in comments.
My effects on you are obvious so that everyone can see
You can see because of the sun!
I'm one of many beings that all have origins the same
One of many stars
Some can kill you easily and some are much more tame
Not sure, maybe radiation causing cancer? EDIT: As explained in comments, some stars have stronger gravity than others and can therefore kill you easier.
I can make you happy any time of day
Day, but not night
As long as the evil grey will just stay away
As long as the moon stays away. Apparently the sun is biased against the moon and calls it evil.
As the eras go by I will have no choice but to eat you whole
The sun will eat the earth when it becomes a red giant. Thanks @HWalters
Then after, I will turn white because I am done and full
It will then become a white dwarf. Thanks @HWalters