npub19lg6tmefu8ydm4tve2zt7agh0t93qw7yuq2m5wc32k5au9lrqf3qk3ehsf (npub19lg…ehsf)
Main argument against a windfall tax is a standard #ruleoflaw argument that laws (and by extension taxes) should be predictable; one might argue that a windfall tax is arbitrary & punishes behaviour that was legal at the time (again retrospective legality is generally seen as not being fair under a the rule of law);
2nd Q.; you set a level for 'normal profits' then impose a windfall tax when profits are by some set margin persistently above that - but could be gamed, of course