Why atheists focus on certain religions

Why do atheists always focus on Christianity?  Why not focus on a much more harmful religion, like Islam?
or...
Why do atheists always focus on fundamentalist Christianity?  Why not focus on more reasonable forms of religion, like mine?

These are some of those questions people ask vocal atheists (in the US).  But to any vocal atheist, a handful of answers are immediately obvious.  Here are a few...

The atheist movement prioritizes social change over academic debate.  The calm and methodical search for truth is a worthy goal, but one also has to admit the importance of actually getting things done.  Religion is not just some academic hypothesis, it's something that actually causes people to kick out their children, oppose LGBT rights, and make poor medical decisions.  If that is something we want to change, we do not criticize the most compassionate and reasonable religions, we criticize the least reasonable, most harmful, and most popular religions.

Atheists are focused on here and now.  This is not simply due to the desire to create change where it will most benefit ourselves.  It is also because we have more power to change the here and now.  Islam is pretty bad, but has the most impact far away.  Local attitudes are easier to change.

It is likely that you are viewing atheists through a filter.  Atheists actually do criticize Islam, liberal Christianity, eastern religions, new age religions, as well as non-religion things like alternative medicine.  But the criticism that actually gets widely propagated is the stuff that's most relevant to people, or most exciting.  For example, I think atheist criticism of Jainism would be vaguely interesting, but not that interesting, because, honestly, I've never met a Jainist in my life.  And I think there is popular appeal in seeing the most extreme atheists and fundamentalist Christians just duke it out.  If people want it, then people get it.

Atheists write what they know.  That means they'll talk about what's in the news they read.  It also means they'll talk about their personal experiences.  Even when atheists talk about abstract arguments, they're often inspired by some real argument they had with someone, or an article they read.  The same is true about most things people write on any subject.

I'm sure readers can come up with other reasons as well.

My advice to people who think atheists are just focusing on straw men: Relax!  If a particular criticism of religious beliefs doesn't apply to your beliefs, then it doesn't apply to your beliefs.