This is a very old argument, rooted in differences in how one believes OSS cooperation is best fostered; through social norms and practices, and/or through legal fiat.

BSD/MIT authors see most proprietary use as a feature — it can drive adoption and contributions that wouldn’t exist otherwise, while generally not directly competing with the original project in the open source commons.

It is considered an opportunity to leverage social mechanisms to garner support and contribution that would otherwise not be available.

GPL relicensing is different, in that it creates a direct rival open source commons with inescapable one-way asymmetry.

The license permits it, but since BSD/MIT authors tend to prefer social norms over legal fiat to sustain cooperation, they don’t see hypocrisy in objecting (even if GPL advocates do).

(I’ve tried to be as measured as possible, but obviously, I fall on one side of the debate, and I’m sure that my point of view leaks through.)