Honestly, I used to think this was dumb, but if you keep an open mind, what's so ridiculous about height classes? Why is weight classes so much more logical? At the least, both have their pros and cons.
A few things we know now about weight classes:
1. They don't really work because fighters not at the same weight at all on fight night.
2. Fighters are missing their weight cuts often and even the ones who make weight, some are not at their peak shape on fight night due to the hard cuts.
3. Fans and fighters talk all the time about the huge disadvantage for shorter fighters, so wouldn't it be worth considering if height advantage is important and creates an unfair playing field as weight advantage?
Going to height classes offers some positives (and some negatives of course)
1. No more missed weight cuts. Despite the impressive height cuts of Shane Carwin, no one has consistently cut height. It would be relatively easy to eliminate height cutting by using a very good ruler.
2. Fighters can bulk up all they want. We will have the strongest and biggest fighters at any height class.
3. A few elite lighter weight fighters with incredible skill will be able to compete with much heavier guys at the same height. This is like the early UFC days.
Anyhow, will never happen, but if someone never watched sanctioned fights with rules before, the concept of weight classes is no more or less ridiculous than height classes because in a "real" street fight, there are no weight or height classes.