If someone is habitually consuming sugar sweetened beverages, replacing those with ASBs will, the evidence strongly suggests, reduce your risk of obesity and various chronic diseases. We can say "just don't consume either" but we have decades of attempting such policies that shows people don't work that way.
Someone who wants to drink a can of coke will drink a can of coke, why would we ban the healthier option?
Someone who wants to drink a can of coke will drink a can of coke, why would we ban the healthier option?