[Citation needed]
The largest problem is the fluff it produces. Saying "Because there are no mechanics associated" doesn't deal with the fundamental problem that calling entire races evil is both weak and toxic worldbuilding.
What's wrong with fluff produced by using CG as a guide to roleplaying my character? What's wrong with the fluff produced as the DM by using alignment as a starting point for how I run NPCs and monsters that aren't important enough to warrant detailed write-ups?
Asnwer: Nothing.
It's in every single statblock. That's clutter. Especially as statblocks are intended to be stripped down to the things you actually use where the rubber meets the road. Your "two words" issue is like saying "it's only a lump of grit" conveniently ignoring that that grit is in the engine rather than in on the road.
So what. Ignore the clutter and move on. It's not clutter for the majority of us that use it.
When I look at the statblock
for an orc it's put in pride of place as the fifth and sixth words. I read fast - and I shouldn't have to train myself to stop reading at word three or four. Which means this visual litter is taking pride of place.
Would it help to move it to the bottom? I mean, you're reading waaaaaaaaaaaaaaaaaay too much into it if you think that it's placement is some sort of location of pride, but whatever. since you're wrong about that, move it lower. You can be happy that it's shamed now, and we can still use it just the same as we always did.
I've said we can make it an optional rule. A rule that appears only within a single chapter that is basically a table would make it equivalent to feats.
It also has to be in the monster stat blocks so we can continue to use it for monsters without having to invent alignment for every monster we play with. In 30+ years of play with hundreds of players, not all of which liked alignment, not one of them was so upset by alignment that they had to stop reading when they got to it. Your personal issues with alignment are your own and have no business impacting the rest of us.
For that matter treating it that way would do what you claim it does as a positive better - it would allow you to more easily find e.g. chaotic evil groups of monsters. So it would be actively better for your claimed use.
How does one chapter in a book help me to know what alignment each monster is?
Having it where it is makes it worse for me. Why are you so keen on enforcing this "optional" rule in my statblocks. Why do you want to make my games and my enjoyment worse?
A minority of players have enough problems with alignment that they stopped using it. An EXTREME minority of you are so distraught by two words that you go to pieces and have to stop reading. You don't design a game around such an extreme minority of players.
If it is in every statblock it is not an optional rule in the same sense as literally any other optional rule in the game - which is kept in its place so people who don't want it can ignore it.
You keep saying that as if repetition can somehow alter reality and make it true. It won't ever be true. All it takes is. Orc - Alignment: Chaotic Evil(optional) and you are objectively wrong. Heck, you don't even need to do that. One sentence in the beginning of the MM stating that alignment is completely optional and you're wrong.