Not the only meaning of "legitimate". There's also "Authentic, real, genuine" and "Conforming to known principles, or established or accepted rules or standards; valid." (Wiktionary) There's a question of acceptability involved here, I feel.
The issue is not one of "monetization" vs. "non-monetization", but one of priorities being driven primarily by the interests of a corporate surveillance capitalist owner rather than what's healthy for the community.
Google's agendas (advertising, amp, etc.) are clear in the design decisions taken for Chrome, and slowly we're beginning to see analogous prioritisation come to GitHub. Expect more to come in time.
I, too, hope that the Belgian government succeeds in this. I guess my point is that it is probably cheaper at this stage for FB to put up a legal fight than to actually implement the necessary changes.
I suspect that it's just too difficult, possibly next-to impossible for them. Tracking is (I assume) baked into every aspect of every system they have, and carving out an exception for one small country is just... exceedingly high effort. Given a large and complex codebase, may well be close to impossible even assuming years of significant effort and cost ("Are we sure we got all the places...?") the only outcome of which (from FB's perspective) would be to reduce their profits very slightly.
I'm not trying to excuse their unpardonable behaviour here, just trying to think unemotionally about what might be going on behind the scenes. Personally I wish they'd stop tracking me - and I have no FB account. I may have to emigrate to Belgium. Good beer an added incentive.
... and the often hilarious scene that ensues when you don't share a common language. Some of my best memories are made of things like this.