Seriously. What's next, are people going to to start *****ing about how people like Marie Curie were basically throwing their lives away for the sake of studying something that ultimately killed them?
And as someone already pointed out friendship with Merrill basically amounts to building up her confidence (by accepting what she does), to the point where she begins to make more positive (herself-wise) decisions and starts to question whether all her work on the mirror is actually worth it when she has you. Rivaling her is basically building up her rebellious side (because THAT's going to work out sooo well).
Congrats, you figured out that she continues working on the mirror whether you want her to or not.
Oh, and Merrill likes sarcasm. Especially around Anders. She's socially inept, but incredibly smart.
And seriously, we're on DA:3 now. DA:O/DA:2's blood magic hype was OBVIOUSLY exaggerated, and one can even argue that a spirit healer could actually be EVEN MORE dangerous than a blood mage if he/she loses sight of her values/morals.
Blood Magic, at least, is an "evil" that we know more about. Considering how Tevinter is not (AFAIK) overrun with demons and how many generations of mages have been using it there then we know that it corrupts only in the sense that power also corrupts.
Meanwhile, all it takes is for a spirit healer to have some sort of breakdown and BOOM. Literally. Cue one of the most horrible wars in Thedas history with such terrible implications that they basically trigger the events behind DA:I.
I think it's pretty obvious that Merrill and Anders are supposed to be a study in similarities (both are mages, both ultimately lose someone very close to them as a result of what they do, both are intent on "saving" their people) and contrasts (a blood mage and a spirit healer, a Dalish second and a Chantry devout, a socially retarded figure who isolates herself from other people and a charismatic figure who works closely with them).
Guess who ends up blowing up the world.
And to answer the OP, I support her in the sense that doing so makes her rethink the wisdom in doing what she does.