One drug is possibly more harmful but is already legal almost everywhere, deeply ingrained in many aspects of Western society and has a history of issues regarding criminalization
The other is possibly less harmful but it is currently illegal/controlled pretty much everywhere and has a niche demand.
I think its entirely reasonable to think that we should not open up a whole new can of worms.
How is the can of worms not already open? The War on Drugs has failed to put a dent in drug consumption habits.
My suspicion why there was an uptick of incidents in NL/Amsterdam was the influx of people specifically seeking those substances out, with little safety education or experience. If they were more widely available, the incidents would be far more diffuse, and likely fall below the noise floor. Plus, wider awareness means better overall substance education and understanding, meaning fewer folks getting in over their heads and acting a fool.
The same "can of worms" argument was leveled against cannabis legalization, and turned out to be overblown, there was no outbreak of reefer madness.
It's not whataboutism bring up other risks that as a society we tolerate, when we are thinking about restricting one.