Do atheists hate religion because it made their families shun them? Is their hatred really just bitterness?

So, religion tears families apart? Thanks for admitting it.

What codswallop.

Firstly, atheists do not all hate all religion - your sweeping generalisation has failed to take into account the individuality of people's decision not to believe in a deity, and how that then impacts on their views. There are plenty of atheists in this world who simply don't believe, but don't 'hate' religion as a whole. There are many, atheists and followers of various religions, who seriously hate some of the hate-filled garbage that is sent our way by some groups within some religions (in my experience, Christianity).

Secondly, believe it or not, most families are quite capable of coping with their offspring choosing a different path to them. My parents, one from a Jewish family and one from a Christian family, were both atheists, and while one of them got some initial criticism, in the long run, it just wasn't an issue.

You see, your fantasies about atheists just don't hold water. Most atheists are quite happily getting on with their lives, with friends, family, a community that values them and that they value. It's not a miserable or bitter life. I do have to wonder, though, if this isn't a form of projection on your part..... as you really don't seem too happy.

My family has never shunned me and the vast majority of atheists are totally indifferent to religion.

Being shunned by their families is a factor. It could be either of them depending on the particular case.

atheists hate religion even before their families shun them.

it depends on how people describe their god they worship, is he malevolent, without mercy, and a dictator, anyone would turn away from that kind of god, but a good christian wont force their God on anyone, as they know it is G-d Himself who elects those whom He wishes to serve Him.