Keith Thurman - The guy was a Light Middleweight aged 18, and is comfortably making Welterweight, aged 28. This guy is clearly cutting a significant amount of pounds to make weight, through dubious means, and inflicting significant weight advantage on his opponents.
Kell Brook - This guy is a heart attack waiting to happen. Holds the IBF title so cant weigh more than 157lbs on fight night. So the mofo is still severely drained when stepping into the ring.
Shawn Porter - A middleweight in his teens, and now he's a welterweight. This guy is a straight up cheat. He is taking something.
These three fighters need to move up to 154 and compete there to get there ass handed to them by men their own size.
I'll tell you a little secret about "cheating" when it comes to weight cuts - you might lose weight to make the weigh in, but it does you no advantage on fight night when you're depleted. More over, I've never heard credible sources say any of the men you mentioned have cheating in their weight cuts - and if they can cut the weight and still fight well 24 hours later, good for them. Cutting weight is as old in sports as weight restrictions themselves. As long as they are content with where they are, it's fine by me.