The lore of blood magic hasn't changed. The problem is the implementation of blood magic in DAO and DA2 by pc characters has never truly reflected the danger/temptation that blood magic poses. I am not saying BM has to be evil, but there are some risks to BM that gameplay does not represent that are shown in the lore and in the books.
But there are two bodies of lore regarding blood magic. There is a relatively small body of in-game fact about it, and rather a lot of in-game opinion. Most of what is said about blood magic is "the Chantry teaches" kind of lore, which can very possibly be substantially wrong.
As far as what we've seen of actual history (not what we've experienced as a character, but learned about NPCs) it seems that blood magic can be very dangerous when used recklessly or out of desperation, but it can also be used in relative safety with caution and control. Malcolm Hawke was able to use blood magic safely, and so apparently was Merrill, even off-camera. Morrigan was at the very least a blood magic dabler, and never had an issue with demons.
I think before you go calling for certain side effect to be shown for all usage of blood magic, you should first be sure that those effects apply necessarily, rather than just potentially in a "worst case" scenario.