HC, dug up some legislation wording used here in the great frozen north were nobody stops flying.
Transport Canada's latest position on freezing rain or drizzle is that it is equivalent to "severe icing". Quote from ASL 4/2009 "Takeoff into known freezing drizzle and/or light freezing rain is outside of the flight envelope for which any airplane currently operating today is certificated. ...".
Interestingly (or practically for operations in Canada), they differentiate between "forecast" icing, and "known" icing. In fact currently the regs 605.30 says
"no person shall conduct a takeoff or continue a flight where icing conditions are reported to exist or are forecast to be encountered along the route of flight unless
a) the pilot-in-command determines that the aircraft is adequately equipped to operate in icing conditions in accordance with the standards of airworthiness under which the type certificate for that aircraft was issued; or
b) current weather reports or pilot reports indicate that icing conditions no longer exist"
There is a proposal to change (b) further to permit more flexibility in operating in reported icing conditions:"b) current weather reports, pilot reports, or briefing information relied upon by the pilot-in-command indicate that the forecast icing conditions that otherwise prohibit flight will not be encountered during the flight because of changed weather conditions since the forecast." In other words, even if icing is forecast, if the commander has reason to believe his aircraft won't ice up along his route he can still fly.
So there you go for all you ice-dummy aircraft commanders. "heavy lies the crown..."