All religions can be called ideas because they are thoughts & observations about the universe which are shared between peoples and are just another unit of cultural transmission. Big bang theory is an idea. Intelligent design is an idea. I think it is perfectly reasonable to call these ideas, and people will subjectively decide which idea fits their perception of the world the best. And I think in a free marketplace of ideas the best ideas will win, and only those who know they won't win will try to seize the means of thought in order to attempt to perpetuate the delusion that they are right. Like communists, for example.