I know people who have been drinking unfiltered stream water for 20 years with no ill effects. The key is to make sure that the water doesn't pass through any human inhabited areas.
There may not be humans or cattle around, but all sorts of wild animals defecate, urinate, procreate, etc. in water. Treat the water (boil, filter, pills, etc.) before using it and you'll be OK.
If I'm in an area where there aren't poison drops and where there is no human interference, I'll take the risk. Outdoor activities are inherently risky.
I've come close enough to dying in the outdoors in other ways that I'm not concerned about getting the small chance of getting the shits from drinking from a stream that I'm 99.9% sure is safe.
It's a matter of applying a bit of common sense. Don't drink the water where there are cattle, or downstream of a beaver dam. Take your water from higher elevations, where the UV light will quickly kill most pathogens (just like a SteriPen!).
Also, giardiasis is not that bad. Get some metronidazol and you'll feel better in no time.
I've done it both ways. Waiting out the diarrhea sucks, but it won't kill you if you have access to potable water. Getting rid of it with drugs requires a significant shake-down from the health care racket in the States, or pocket change elsewhere. In any case, you are unlikely to have to make the choice more than once in your lifetime if you exercise a bit of caution and common sense.
I know people who have been drinking unfiltered stream water for 20 years with no ill effects. The key is to make sure that the water doesn't pass through any human inhabited areas.