Quid pro quo?
If carriers could get away with this, one would expect the reverse to be true. Overbooking should then be far more expensive, with greater compensation to PAX.
This is just another dubious revenue tactic. If you for some reason don't make your final leg, they will put a standby in that seat and in effect get paid twice for that seat. If flight is less busy, they still get dollars for an empty seat.
I cannot see any judge with common sense and a moral compass giving carriers a pass with this re-pricing tactic. It's immoral.
Money making corporations will more or less engage in dubious or criminal tactics to make profit if not regulated and reprimanded. That's a given and proven over and over again historically.