|laziness, impatience, and hubris|
Should you need a licence to design a freeway bridge? An aeroplane? A skyscraper? A real-time train switching control system? Pacemaker firmware? Insulin pump?
I am a licenced professional engineer (yea, whoop dee doo, but I have had some experience with this) and everywhere I've worked in my field (i.e. not software!) there have been many unlicenced staff working under the supervision of a licenced engineer. Most of the time this is required by law, but sometimes it is simply required by the client, who wants some assurance of quality (and no, ISO 9000 ain't gonna give you a better bridge).
Granted, the safety argument is a no-brainer, so let's just consider costs. A poorly designed road may be safe enough, but it might not last very long, meaning higher maintenance costs and capital replacement costs, both of which can be estimated fairly accurately. What does a bug in a banking system cost? An inventory control system? Is it because these are harder to quantify (that is if anyone wants them quantified which I doubt) that few seem to care?
Like it or not, I think software will become regulated as a profession sooner rather than later, and it's up to all you who think of yourself as software professionals to see to it that standards are set, met and kept. Just as a clarification, licencing doesn't have to mean Big Brother, as most professions are self-regulated under powers granted by the government, but not controlled by government. Sure it takes away the sort of microchip cowboy image that many enjoy, but that can be reserved for your time off. When society is paying the tab, it eventually learns to get what it wants.