By ecologically problematic, do you mean that if many passengers opt to fly with adjacent seats empty it would transitively mean that more flights would be needed to meet the demand? (if that is the case it absolutely makes sense !)
That's what I meant yes. Of course if it's applied onlx on routes where utilization is low a priori, my argument doesn't apply.
Doesn't the same argument apply to the existence of business class? Since to a very large extent, what you're paying for in business class is the extra square feet of cabin space.