Of course people have a right to voice their opinion. In this instance, however, it's clear that certain posters go out of their way to find even the tiniest thing to trash William and Kate for. They have been determined to paint this tour as a failure since long before the Cambridges even left the UK. Had they waved, the complaint would have been that they didn't wave for long enough, or they didn't smile enough, or that their smiles were fake, that they didn't pose for this one woman to get a clear picture of them.
I can understand the frustration some here feel at posters who only ever post negative and unfair criticism, not infrequently with a fairly nasty tone. As we all know, there are other royal forums on the internet where people delight in those sorts posts, I didn't think TRF was one of them.