The debates I listened to was not on whether they should be allowed to post the ads. People were generally agreeing on freedom of expression
Rather, it was whether the ad content was hateful and misleading.
For example, most believers I know are living a happy worry-free life vis-a-vis the existence of God.
The ad implies that believers are in a constant state of worry which is not true.
Conclusion: Atheists could publish whatever they want. In fact, this type of ad campaign only preaches to the fellow atheists as true believers would not be swayed by their flippant approach to God