Do people filter reality through the prism of their agenda?

Absolutely! Why do liberals think that only conservatives do this? People also filter issues through the prism of their psyches.

Actually, I think I know why. When a liberal considers ANY issue, he considers his viewpoint as normative. This line, which is way left of center, is to them the center. Everything to the right of that line is "conservative" (which is how they labeled Bill Clinton "conservative", as well as Barack Obama), the line is "Mainstream", and the few things remaining on the left of that line are just "liberal" to them, never are those things "radical" or "nutty".