Lese majeste: An offence against the "dignity of the sovereign". Like painting a moustache on their statue, calling them a poopy-head, or criticising their performance as a ruler. Strangely, it was the last one which tended to be the most vigorously prosecuted.
Citizens of modern liberal democracies find the idea of their rulers having some special dignity which renders them immune from criticism to be laughable. We no longer believe that our politicians are somehow better than us and automatically deserving of respect (the obvious exception being the Americans, but their Presidency was designed from the outset to be a sort of elected monarchy, so its hardly surprising). And so over the years, the "dignity of the sovereign" has been transferred to the State, and thence to the flag.
However, one of the underlying axioms of those democracies is that nothing is sacred. Everything is up for grabs, to be questioned, criticised, and (if necessary) burned in effigy. So why the hell, after all these years, are we still protecting the "honour" of the flag? Doesn't it seem too much like protecting the "dignity" of Helen Clark from people who would deface her official portraits?