The difference between a stranger sending you a message that you might be interested in at a very low volume level, no repetition, just sending it to very few people, and that being done as spam - those things get close enough that you want to be careful never to filter out something that's legitimate.
The very admission of the need to harmonize is an admission that the burden of proof is on the narratives, not on those who doubt them. What harmonizing shows is that despite appearances, the texts still might be true.