You can find an em dash in my comment history if you're curious. Despite what could be said about poor sample selection, consider the imbalance of the argument being made: the frequency of em dash use is disproportionate to the suspicion thrust upon a sample of writing. I.e., a single em dash is suspicious, regardless of how many times it might show up. Therefore, it's more likely that someone who uses em dashes—even if only rarely—will self-select to respond to a thread like this and feel compelled to defend themselves.