Mostly I think that people "approaching this from a security perspective only" often forget that by fencing in the(ir idea of the) current status quo, they often prevent beneficial evolution of protocols as well, contributing to the Internet's "ossification".
folk do not always get the implications of the internet being a 'disruptive technology,' and that this is a good thing which needs to be preserved and even enhanced. they use skype and want to block ports. it's rampant. the old siliness of blocking tcp/53 is just one of the corner cases that keeps popping up publicly. try using this year's crop of innovative apps from behind some corporate firewall. packet/port xenophobia overrides the users' desire to be productive every time. it departments are paid to minimize cost and risk, not maximize workers' productivity. randy