Why do atheist attack Christians over a God they don't believe in?

Why do certain pious Christians feel that presenting a view contrary to theirs in any context is necessarily an attack on them? 

Yet, many Christian sects perceive it their duty to push their (views on) God on the unbeliever and the unwilling, often demonizing other thinking, in terms like heresy or blasphemy, referencing a deity they themselves have not materially substantiated. 

 Is it that they truly don’t recognize their unwelcome proselytizing as Intolerant to the sensibilities of other people, or that they simply don’t care how hypocritical they are... ?

 In addition to the many, many good works of faith we could cite, a case can be made on the immeasurable suffering perpetrated by the parties of Christianity (in this case) through the centuries, that it is long past time these iniquities get called for what they are. I haven’t heard of many genocides that were instigated by atheists...

 Debbie, there is no doubt in my mind you are a nice person, and probably a fine mom, wife and a good citizen. Playing the Martyr Card as a position of doctrine is a species of organized intolerance. Right or wrong, intolerance perceived is intolerance received. 

 It doesn’t seem at all unreasonable to conclude that the religious impositions on the infidel are (at least) no better than the reciprocal.