I make 10 gallon batches, so occasionally filter one keg and not the other. When I've done triangle tests in opaque cups with those beers my tasters consistently pick the filtered beer over the unfiltered one.Are your unfiltered beers clear? If you are having them compare beer with starch or yeast in them to a filtered beer, it wouldn't surprise me if they preferred the filtered beer.
If both beers were clear, I'd expect some styles to suffer reduced flavor from the filtering process. Is it possible your tasters just prefer a milder, less flavorful beer?
When we have done this experiment i tried to make it as legit as possible. It's not green beer; i wait 6 weeks or so to let the unfiltered one settle out. The unfiltered keg is clear, the filtered one brilliant. If I handed you a glass of each individually (not side by side) you might not even notice the difference in clarity. Side by side you can tell.
My tasters are not neophyte bud light drinkers or anything like that. They are home brewers and experienced beer drinkers with wide ranging tastes. I should dig up some notes from some of these sessions to see exactly what phrases they used.
I suppose some beers might suffer, but I take that as a recipe issue. If I find my 10 day pale ale is flabby after filtering, the I will add more hops next time! Anyway, I find it a useful tool to have in my arsenal, especially when I come up on events for which I need lots of beer on hand in short order, and have to travel to get there.