I really do not know why atheists are so strident. It appears that over the last few years they have absolved themselves of their requirement to be polite. While many of the atheists I know and interact with are quite polite, there is a large and growing number of quite aggressive atheists. This is not to say that many people do not have good reasons for disliking religion, there certainly are good reasons.
What the strident atheists do not seem to understand, really at all, is that debate does not favor their position. I personally attribute the rise of atheism to a general, but quiet, lowering of the importance of religious thought in society. Many young people today, take the message as be good, figure that they got it and don't really see the need to go to church on Sunday to appreciate it. That is the message that has been going out from mainstream Christianity for decades. It has been this factor, really more than any other, that has prompted the rise in atheism, agnosticism and apatheism.
While this has been happening, the debate really has gone to the extremes. Atheists have become increasingly intolerant and seem to have laid siege to moderate religious people. Before I took to studying apologetics in any serious way, seldom did a week go by when people would attack me, a Catholic backslider with a center left political membership (who lobbied for rights for same-sex couples). The new atheists basically decided it was time for me and those like me, to go.... I have to say, that I disagree.
What is striking to me, is that it was the general apathy towards religion, especially in my own country, that really produced the downward spiral in numbers. People in Australia really do care more about the football than politics and religion. The problem is, that the new atheists picked a fight, when it was the peace that was killing us. That is ok though, because now its pretty much game on. Atheistic philosophy peaked with Russell and Ayer and the subject been dominated the Christian resurgence ever since. The fight is at the wrong time for atheism, they have next to no good arguments, it probably has never been a worse time to be an atheistic philosopher than now (at least since St. Thomas Aquinas put pen to paper).
Secondly, they completely missed the point of the martyrdom of St. Steven. When it was no longer safe to be Christian in Jerusalem, the Christian faith exploded all over the place. People could not hide anymore and as a result, the didn't.... So basically, thank you new atheism for shining a light on the Christian faith... its the best opportunity we have had in decades.
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Life is real ! Life is earnest!
And the grave is not its goal ;
Dust thou art, to dust returnest,
Was not spoken of the soul.