Ignorance may not quite be the right word. It seems to be more a mental refusal to deal with something unpleasant.
Someone I know used to be fond of saying that most of the world's problems are caused by weak people, not evil people. (Weak in this context meaning lack of strength of character, compromising principles, hedonistic, unwilling to stand up to bullies, etc.)
I think that this religion would have died out long ago, if people within it and outside it had the courage and conviction to call it for what it is, more often.
So in my opinion, "ignorance" is not an excuse. Worse, it is a fundamental part of the cause.