Oh, it’s definitely not. In fact, the vox populi (voice of the people) was the primary test for canonization in the early Church–and although the process is a bit more involved these days, it’s still the first step. Usually it is the local church where the saint lived that develops a devotion to him or her first. Beatification (declaring the saint “blessed”) is a permission for the local church to publicly venerate that saint–in other words in the official liturgy and calendar. Canonization, the final step, is the affirmative declaration that the saint is in Heaven (rather than a permission to believe so) and to be venerated as such by the universal Church–and then the Saint can be included in the universal calendar and liturgy.
The local bishop and ultimately the Pope are responsible for suppressing any popular veneration of individuals who may not be worthy of it (if their life was not an example of Christian virtue). However, the sensus fidei (sense of the faithful) is pretty good when it comes to this. I’m sure there are individuals here and there who stray, but I’ve never heard of an instance where the faithful were venerating someone that didn’t live a saintly life and had to have their devotion suppressed.