Sandia,

I don't think this is a group that has much personal bias. I've looked through the old posts of the more experienced backpackers here and I've seen a gradual shift in their ideas as they got more experience. In some cases, their advice is the complete opposite of what it was last year.

In your case, you are focused solely on Giardia as a source of the intestional distress. Let's say there are 10 bugs that cause intestional distress. I consider any study that declares water "safe" because of the absence of just one of these bugs is flawed.

In my opinion, I have two choices. I can carry a filter or I can carry more toilet paper. I prefer the filter.