Rabies wrote...
The taint isn't something that interacts with your mind in the way you're thinking. The Joining offers the participant immunity to the worst effects of the taint. In particular the becoming a ghoul or immediately dying to it.
I actually think, especially after the events of Dragon Age II, that this is mostly chantry propaganda - but with a seed of truth. I believe that the Tevinter Imperium WAS responsible for the creation of the darkspawn, but not in the way that the chantry proclaims. I think they metaphorically stepped into the Golden City and into the Maker's realm by attempting to create life...
We've already seen that they weren't adverse to experimenting on living beings. This is what brought about the mabari, and Fenris' lyrium markings. I think that that thaig you come across in the Deep Roads on Hawke's expedition is actually an old Tevinter Imperium temple or research facility. If you notice, that lyrium idol looks suspiciously like the Architect or some other manner of darkspawn.
I believe that the darkspawn were CREATED by some mages from the Imperium, probably using blood magic and the magic of their Old Gods to try and create life from nothing. It was an experiment that went horribly horribly wrong.
Oo I love the idea of the Deep Roads expedition actually uncovering an ancient Magister testing ground! It would explain the Profane, and why they can be posessed by demons despite being made of rock. And, well, EVERYTHING about it.
Anyway, I think I started my topic thread poorly in terms of explaning myself! The Mages/Darkspawn/Anders theory I meant to test out was basically as follows, in timeline form:
1) Incredibly powerful Mages make it to the Golden City in the Fade, and turn it into the tainted Black City. They return as the first darkspawn, tainted by this Fade-connection.
2) Fastforwards and we have Grey Wardens, including lots of garden variety Mages who aren't affected by the taint in any special way
3) A freak magical accident traps a very powerful Spirit of Justice outside of the Fade, severing him from it in a way which prevents him from returning and rendering him very unique (spirits don't normally leave the Fade ever and who's to say what power they potentially weild)
4) Happy-go-lucky and slightly dumb Grey Warden Mage Anders joins with Justice
5) Boom... just as the first Mages found a way into the Fade, Anders becomes unconsciously powerful enough to "bring the Fade into our world" - joining with such a unique spirit actually makes him far more powerful than he even knows
6) The taint comes into play somehow in influencing his revolution to free all Mages, as the little bit of darkspawn in him turns Justice into Vengeance and turns them into a killer machine in pursuit of what, eventually, could be a second Magister imperium breaching the Fade.

One extra question is:
what on earth was in that Chantry bomb?? It's well established that it takes a powder keg full of lyrium or blood magic for huge massive effects in the Dragon Age universe. The Chantry seemed to completely rise up and get decimated molecule by molecule in a massive magical implosion - a few bits of sewer crap and bones wouldn't be able to accomplish such a feat, and nor would Anders use blood magic.... so what the heck kind of power did he harness to do that? (Something very old, and Fade-related, is my theory).
Yes, I'm totally overthinking all of this. I just like to analyse and theorise this stuff. It's interesting.