And you're right, claiming something does not make it so. What makes it so is all of the data supporting it, which is readily available to anyone who actually cares about this topic (up to you if that's you).
Who is arguing that DEI is ineffective when properly implemented (what does "properly implemented" even mean, concretely?).
> they both fly in the face of a whole lot of data
You keep referencing this data... Where are the metanalyses that show concretely that DEI programs are effective? To be clear, I'm aware of and believe that increased diversity makes organizations more robust, but again that's attributed to viewpoint diversity and it's not at all clear to me that modern DEI programs deliver on that viewpoint diversity. It's not even clear to me that there is widespread consensus that "viewpoint diversity" or "organizational robustness" is a goal of these programs--one definitely gets the impression that the primary goal is diversity of identities with little mind paid to the impact on viewpoint diversity or organizational robustness.
Here's HBR (https://hbr.org/2019/07/does-diversity-training-work-the-way...) talking about whether or not diversity training programs are effective; note that the implication here is that the goal is ideological agreement--they're not even looking for viewpoint diversity:
> What did we find? Let’s start with the good news. The bias-focused trainings had a positive effect on the attitudes of one important group: employees who we believe were the least supportive of women prior to training. We found that after completing training, these employees were more likely to acknowledge discrimination against women, express support for policies designed to help women, and acknowledge their own racial and gender biases, compared to similar employees in the control group. For employees who were already supportive of women, we found no evidence that the training produced a backlash.
Regarding the research into DEI, a lot of the measures of its efficacy (that I'm aware of) hinge on Implicit Association Tests which are a famously plagued with issues (https://www.vox.com/identities/2017/3/7/14637626/implicit-as...).
> Who is arguing that DEI is ineffective when properly implemented (what does "properly implemented" even mean, concretely?).
Nearly everyone in the comments here, are you blind?
> Where are the metanalyses that show concretely that DEI programs are effective?
Here's one that took all of 5 seconds to Google:
> Results from 65 studies (N = 8465) revealed sizable effects on affective‐based, cognitive‐based, and skill‐based outcomes as well as interesting boundary conditions for these effects on affective‐based outcomes. This study provides practical value to human resources managers and trainers wishing to implement diversity training within organizations as well as interesting theoretical advances for researchers. Practitioners have quantitative evidence that diversity training changes affective‐based, cognitive‐based, and skill‐based trainee outcomes. [0]
[0] https://www.researchgate.net/publication/263597048_A_meta-an...