Personally I want to be as unobtrusive in the wilderness as possible. There seems to be a lot of focus on, even fanatical devotion to, leave no trace. While bright colors aren't technically leaving a trace once you take the tent down, you are unnecessarily polluting the view of anyone else that happens to be there. It's kindof like jumping up and down shouting "Here I am, here I am.".
Most of the time, being unobtrusive is merely being polite to others, but there can be times it really matters. One obvious case is stealth camping. In places where the land is tightly controlled, like New England, it's not always easy to find a clearly legal place to camp. Sometimes the best alternative is to go a few 100 feet into a patch of woods, be as unobtrusive as possible, and of course have as little impact as possible.
Theft or other illegal activity is another, although admittedly minor, issue. One time I was swimming with some friends in a lake by the side of the trail. We put our packs down by the edge of the water. When we got back, one of my friends' pack was gone, and another one had been rifled thru. Mine was completely untouched only about 2 meters away. The only difference appeared to be that mine was olive gray-green, and the others were bright colors. It seems the thieves simply didn't notice my pack.
I'm currently looking to replace a small backpacking tent that got lost in airplane luggage last summer. I'm very dismayed by the many options that only come in bright obtrusive colors. Those are non-starters for me. Fortunately some companies get it and either offer a color choice or a single more muted color.