I'm guessing a lot of them also did not have any idea what happened to Meredith. They didn't see it, for sure. Only a small handful of people saw it. It's mostly all rumor passed through multiple hands, and who are you most likely to believe? Probably your superior, who is telling you that the red stuff is just as good at curing your withdrawals and even more powerful for fueling your abilities. Those rumors about Meredith are just lies created by the mages to discredit the work of a great woman, after all, right?
I was hoping for the sort pitty route. The devine had used her influence to cut off rogue templars trading with dwarfs, in an effort to stop the war. Meanwhile mages were engaging in hit and run attacks stealing or destroying lyrium stockpiles.
Lyrium stockpiles depleting, In desperation they sent out scouting parties one of which found the highlands and reported enough lyrium deposits to supply the army as well as a defensible fort.
And so a the main body of the rogue templars set out to relocate to the base in the highlands. By the time they arrived they were so exhausted and racked with lyrium withdrawals (having used up the last of their supplies on the journey) that they did not care it was red lyrium that they had discovered.
I imagine one or two of the less lyrium addled yelling at them to stop, wait it's red lyrium and being completely ignored as the troops ran past them.