No need for FUD. Symantec for many years led shoddy certificate validations. As a result of many audits finding inappropriately assigned certs the security community at large decided to just stop trusting them rather than continuously find issues in audits. That being said the audits had already been done, the harm of just immediately distrusting the CA wholesale would be orders of magnitudes more than the harm of whatever cert assignments slipped though the audits. A target date for the distrust needed to be chosen, at the same time the security community had been shifting to a maximum of <3 years on TLS certificates and about the same for code signing certificates with a preference they be even less than that farther in the future. The combination of these 2 goals to harden certificate trust going forward leads to the reasoning of why distrust it after all of these years, any certificates that were trusted prior to the distrust of new Symantec certs should be well expired.

Clearly quick reaction is possible if deemed necessary, new certs were almost immediately untrusted following concensus on action against Symantec. Should the situation have been more dire (e.g. a leak of the CA keys) a more dire course of action may have been warranted.