The idea that a push for diversity is somehow in conflict with a meritocracy is deeply flawed because it relies on the idea that people with diverse backgrounds either haven't shown they are capable or that there are no people with diverse backgrounds that are capable. A good diversity program does two things:

1. It identifies and removes certain unnecessary credentials that might rule out people with diverse backgrounds. Requiring a college degree for applicants when a degree provides no benefit on the job is one example.

2. It makes an active effort to find and pursue diverse candidates. Odds are there are plenty of people who are competent enough to do the job. Let's imagine you are hiring 5 engineers from a pool of 100 qualified people. If there are only 10 diverse candidates in that pool and you just hired the first random qualified candidate you find, there is roughly a 60% chance that you end up with zero diversity on the team. If you actively work to get diverse candidates to apply and maybe get 10 additional diverse candidates added to the previous pool, you can still hire the first random qualified person but your odds drop to roughly 35% of having a team with zero diversity.

TL;DR - You don't have to hire less qualified people to have diversity, it just takes a little more thought and effort to make diversity a priority.