The Reason Rally is not about eradicating religion. There is a difference between wanting a secular government and a nontheistic government. A secular government is one that gives no preference to any religion or to non-religion. This allows the government to remain neutral and to protect all religious belief. America’s great religious diversity is best protected when the federal government to stays neutral about matters of religion and ends special privileges for religion in law.Sure, people can work towards "eradicating" (not the best word, but it will do as long as it is not read as implying active persecution of the religious, but merely persuading) religion. But it's not what the Reason Rally is about. It's about secular government, a secular state - and that's not a great secret.
A great diversity of people should be able to get behind that. Many religious people should be able to get behind it, as a matter of fact, though I do accept that this particular event is primarily a rally for non-believers to call for a truly secular America.
Secularism isn't something that only non-believers can support. Generally speaking, it is good for believers as well - not all of them, always, in all circumstances, but very many of them, perhaps the majority in Western countries, in current circumstances. Secularism has a lot going for it apart from its appeal to those of us who reject religion.