Parkour becoming mainstream is inevitable, and most arguments given as to why it shouldn't happen are illogical, very biased, and quite naive.
It seems to me that since Parkour is so new, we as a culture are trying to distinguish ourselves and stand for something. Many of us want to keep this a pretty little sport with a lot of deep philosophy, and many of us would think competition/publicity would be harmful to that. Haha and I don't think we have any rational reasons why.
Look at other sports/disciplines that started of as a very passionate, deep practice: martial arts, skating, surfing, rock climbing, etc. Has competition ruined them? Nope, if anything the publicity has nourished the sport.
I would really like to see anyone present a legit argument against this thought.