Young people have ideals and tend to chance their opinions as life goes on. Those who were in favour of a republic as teenagers or in their twenties often start to appreciate the monarchy in their 30's or 40's. Sometimes because of what the monarchy brings and stands for but just as often because they see how politics works and are glad at least the top job is out of reach for a politician.
With an ageing population in most if not all European monarchies the royals have little to be afraid of.
Previous Message