The difference is that a suggestion is backed by a rational reason. A suggestion can answer, reasonably, a ‘why?‘ counter-query.
Everyone is entitled to their opinions. Many feel it their duty to impress their opinions upon others. These opinions, specially when they are about others’ actions, may* be freely discarded.
Everyone is also entitled to give suggestions. However, suggestions ought to be listened to when they are presented along with the rationale, the why. They need not be agreed with, they need not be heeded to, but they should be listened to and pondered over.
*should