And 'people have been cutting weight forever' is a very valid argument in the fact that for decades wrestlers, boxers, judokas etc. have been part of a system that works. A fighter gassing because he cuts too much is his own problem and his own decision. And its been that way for the longest time. He is to blame and no one else. Renan Barao has trouble with his performance after cutting. He should move up. Johny Hendricks cuts more than 20 lbs. He makes weight and performs admirably. He should stay where he is. Chael Sonnen has said hes had to cut 20 lbs. He did it every single time and despite his faults has never had cardio issues.
There are fighters who cut and rehydrate (with IV's) and are ok to perform and have little issues doing it again. There's a guy at my gym who is 5'6 and a short reach and walks around between 170 and 180. He cuts down to lightweight and rehydrates with an IV. Asking a guy like him to fight at 170 considering his body size would be unfair and by everyone's admission not as competitive.
Any person suffering from a weight cut is at fault. Not the rules or regulations. Weight cutting is a fighter's responsibility and prerogative and if he does it right every single time, no one has the right to tell him otherwise.
It's a valid argument IF IT WAS TRUE. It's not.
Judo is same day weigh in 1 hour before competition. They are governed under WADA and nobody does extreme cuts or is allowed to use IV's.
Wrestling has moved away from extreme cuts. They have hydration limits at the high school and collegiate levels. They are also governed under WADA in international competition (Olympic). Nobody uses IV's in high school or NCAA because nobody cuts that much anymore due to month long hydration tests. And nobody is allowed to do it on the international competitive level due to WADA.
Amateur boxing also falls under WADA (Olympic and international). They are not allowed to use IV's.
As it stands now, of the three examples you've given only Professional Boxing and Professional MMA allow IV's and extreme weight cutting. And in the case of boxing, the boxers spend their entire careers NOT using IV's to make weight prior to going Pro.
If they instituted IV bans in professional boxing, the boxers would hardly notice. They'd simply return to the practices they grew up with... IE, WADA/international competition.
The institution of IV bans in the UFC isn't like some sort of doomsday scenario. What you'll see is that guys who gas in the 3rd will simply have to adjust their body mass to reduce the water cut, or they'll get better at orally rehydrating, or they'll change weight classes.
There will be a short adjustment period and then it's back to business as usual.