If they can make weight then they get to fight, despite how much they had to cut. Cutting a lot of weight always has negative consequences, a lot of the time just as much consequences as benefits from having a size advantage. Gleison Tibau isn't wrecking the LW division cuz' of how much he cuts, Anthony Johnson wasn't ruling over the WW division cuz' of how much he cuts, and Bigfoot Silva isn't destroying every HW that crosses his path just cuz' he has to cut to make 265.
The only real argument there are for having weight-cut limits is for the health of the fighters, and even then when you look into the details of training and cutting weight, then if you do it properly it's not gonna do any more damage to your body that stepping into a confined area to fight another person's gonna do. Urijah Faber said that he has to cut 20 pounds to make BW, and he just figured out the science behind how his body works and is able to make the cut much easier-- two things I recall him saying were that he sweats out 6-8 pounds of water every day during training anyways, so the trick is to just trick his body during the week of the weigh ins by ingesting more electrolytes and stuff, and that a lot of fighters do a water-only cleanse during the week, which isn't as healthy as drinking a coconut water or something cuz' a pound of liquid's a pound of liquid, but one way you get some nutrients from ingesting it and your body isn't as drained, whereas the other you get nothing out of it. Also, the way he described it made it seem like that was only the tip of the iceberg, and that there's a lot more science and shit to cutting weight than just that.
