There's a lot I disagree with here:
1. Non-union shops aren't meritocracies. The most "meritous" employees are also the kinds of employees that will work for table scraps and the "privilege" of doing what they do. Those folk make up the lower half of any org's tree. That's just good economics, try to argue otherwise to your shareholders and you'll get laughed out pretty quickly.
It's the folk whose main motivation is their paycheck and/or the power trip they get from pushing around folk who make up the upper half. There are just far too many obstacles and disinsentives to climb that ladder barring those motivations.
2. Everyone wants a meritocracy until they get one. Meritocracies make for terrible work environments for 90% of people in the org. It becomes a tyranny of those willing to perform metrics-hacking or win the "sleeping-at-work" olympics.
I'm not saying unions don't have their problems, but the idea that they are bad because they eliminate some intrinsically good meritocray that inevitably forms in their absence is among the worst arguments you can make imho.