So is it now OK for groups of us to come visit you in your places of worship and do the same thing? Atheists have studiously avoided this in the past but you seem to want to up the ante.” ~Email to TrueReason.org

Yes. Please do. We invite atheists to our churches. In response to strong demand, True Reason is planning the first annual Atheists at Church DayRatio Christi is one of the organizations supporting TrueReason.org, which is coordinating a response to the secular “Reason Rally” in Washington D.C. Atheists in the blogosphere are contending that Christians should not attend the rally. We have taken the feedback from atheists quite seriously. They have suggested that if we plan to attend their The Reason Rally, then we should expect atheists to attend our churches. Since we still plan to attend The Reason Rally, we want to take the appropriate step of making sure that we warmly welcome atheists to attend our churches to open up a reasoned discourse. At most churches, atheists are welcome every week. However, we wanted to offer a special invitation to make sure they know they are welcome. 

To support this effort, TrueReason.org is proposing that churches across the country open their doors to atheists for an event to begin discussions between Christians and atheists. Specifically, we are calling on churches to coordinate an Atheists at Church Day. Details may be found at http://www.truereason.org/atheist-day/. We hope that many churches and many atheists will participate.

Well known atheist, PZ Myers wrote on his blog, Pharyngula,

I’m beginning to feel like my long-standing personal policy of not intruding on their church services needs to be questioned, because man, is this ever arrogant and obnoxious.  

So that Dr. Myers knows that he also is welcome, a personal invitation has been sent to him inviting him to church. A copy of that letter is attached below. This is a sincere and standing invitation and we hope that he has an opportunity to take us up on the offer with the desire that he will take advantage of the opportunity to ask questions relevant to his disagreements with Christianity. As reason is the premise of the rally, we desire a reasoned dialogue.

Of course we want this interaction to be done in a respectful way. Several of the responses to the Christian presence at the rally seemed to suggest that they are expecting, and thus want to respond with, belligerence.  

Perhaps atheists should show up at your Christmas services and debate the likelihood of a virgin birth? ~ Reasons For God Facebook Page

So, would you be ok with an atheist showing up at your church and “preaching” to the congregation about how the bible is unreliable and self-contradictory?  ~ Thinking Christian blog

No, we don't think it would be appropriate to interject in the middle of a church worship service with contrary views. Similarly, we will not be shouting out questions to the audience or speakers at the rally. We certainly will not be rushing the stage and trying to grab the microphone as is an occasional strategy of progressive activists. There will be no attempt to disrupt the day's events. There will be an attempt to engage willing people in dialogue about the rationality of one world view versus another.

Neither will TrueReason be there to demonstrate against the right of the secularists to gather. That right is firmly established, and is something we hope would be granted to us in similar circumstances. An atheist has a right to meet in private or in public. So do those of varying religious beliefs. Of course, meeting in a public place brings with it certain expectations. There are obvious reasons that the secularists are meeting on the National Mall in Washington D.C. as opposed to elsewhere. Certainly, the size of the location allows for many to participate, but there are other private locations where such a rally could be held. This does not seem to be the main reason. One of the sponsor's press releases says that their intent is 

to unify, energize, and embolden secular people nationwide, the Reason Rally is a FREE event that will combat negative stereotypes about nonreligious Americans.

Another location on the website says the event is meant 

to deliver the good news: “We’re huge, we’re everywhere, and we’re growing.

. . . secularism is coming out of the closet. . . . The purpose of this particular rally will be to advance secularism (in the broadest sense of the word) in society.. 

Those are all very ​public goals for this rally. If the organizers had rented a private stadium and invited only atheists it would be much more reasonable to expect those with countering views to stay away. Hosting a religious worship service in a private church building is a much different scenario than "coming out of the closet" on the nation's public lawn. Historically, this has been a place of public gatherings to attempt to influence society. From their own words this is precisely what the Reason Rally is also trying to do. There is every right then for others to make a public, though contrary, appeal. Again, from their website we find that one of their explicit goals for the rally is:

Legislative equality. Secular Americans can run for office and adequately represent theists, just as theists in office can represent their secular constituents proudly and openly. We deserve a seat at the table just like theists, and we hope this rally can put our values in the radar of American voters.    

If they are putting themselves in the political sphere, they have to expect the attending responsibility to publicly contend with ideas dissimilar from their own.

Furthermore, it would seem puzzling that people associated with a "Reason" Rally would object to those that wished to come and enter into rational dialogue. Of course, they may say that what we have to offer is not rational. That would seem to be begging the question until they have heard what we have to say. What do they have to lose anyway? If we are irrational 'mindless parasites' then it would seem to be to their advantage to have us show up and demonstrate to the watching nation how truly mindless we are. To be confident in a good argument is to be unafraid of a bad one. 

So, let's consider one question posed to us after Christian attendance at the rally was announced.

A question if I may; What will be the response of xtians when we (Atheists) start setting up booths at your gatherings and/or churches? ~ Reasons For God Facebook Page

Setting up booths in churches? No. Setting up booths at a public Christian rally on the National Mall? Sure. Coming to a public event to reason with Christians. Yes. Coming to church to respectfully reason? Please! That's what we are hoping for from the proposed Atheists at Church Day.