Beside what those cultists preached, I found no other explanation of where that dragon came from. Dragons are supposed to be extinct at this age.
Regardless of who says what, I think defiling the ash is inherently evil. Dalish worships the old gods, while the rest of the world worships the Maker and Andraste as his deliverance. I think Bioware did a fantastic job in relating a fictional world to the harsh reality of the world. I am not going to Islam or Christianity, but the morale of the story is:
- No matter what you choose to believe, or not believe, it matters little to others. People stand by their faith, and will do anything to defend it because it is their guidance and spiritual support that carry them all this time. It is best to respect that belief from others, as you hope for them to respect yours. The cultists may carry things a tad too far, but religion itself is not at fault.
- People interpret religions differently. Unlike laws or others, there is no solid copy for you to compare to, to enforce, nor to even verify. From time to time, there are agencies or organizations who stand out with much credibility to shape religious teachings into more vivid understandings, and more standardized and applicable to modern day's culture. But look, the Chantry, or the Cultist, all have their claims. And who else can verify or prove them wrong one way or another? They are also humans, with beliefs, stubbornness, ambitions, malice, etc... But just because a few Holy mothers went rogue, or certain Cultists twisting religions to their own will, it is not enough to discredit that religion as a fluke.
Andraste herself maybe just another person who happens to be there at the right time and right place, if you want to look at it that way. She did something, and many generations later people retell her stories in different versions, and we simply have no way to verify without a time machine. A group of people decided that she is of something holy, and worth worshiping, who are we to say otherwise? True, you may not have to worship her, but that does not mean you should consider defiling her ash and call it "OK to do". Once again, it may be just ashes to you, but to others (and a lot of others) it means a whole lot more to them.
So no matter how we look at it, just because some people that went against popular belief (thus earn the title Cultist), they may have come from a true and noble group of priests a few generations back. And here we decide Andraste is bad.