one problem is, with a brakeless fixed gear, if you have a problem stopping in time for whatever reason, it's not just YOUR problem. it's a problem for whoever's in front of you, behind you, trying to get out of your way or trying to avoid hitting you or anyone else who's reacting to YOUR situation. so in that sense I think it's kind of a safety hazard and selfish. dangerous for other people besides yourself, which should be a consideration for any rider.
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"Think of bicycles as rideable art that can just about save the world". ~Grant Petersen
Cyclists fare best when they recognize that there are times when acting vehicularly is not the best practice, and are flexible enough to do what is necessary as the situation warrants.--Me