Ain’t a thing wrong with dialect, dude.
Only if you assume quaint regionalism take precedence over the actual owners of the word.
Calling it “Legos” is like telling someone they’re not pronouncing their own name correctly.
My habit is to refer to a single piece as “a Lego”, and a group of pieces as “Legos”. However, I am also aware of the official position of the company on the matter, and while I do not give companies in general any particular deference over language, this specific company has brought me enough joy over the years that I feel that I ought, out of gratitude, to respect their wishes on this matter, and so I attempt, when I don’t slip into habit, to refer to them as “Lego pieces” or the like.
That’s cuz you took the s from legos and stuck it on math. 
The word legos is an abomination. Thus saith the Lord.
It sounds silly.
It sounds even worse than the OP’s comparison of “deers” or “mooses”.
Lego is like fish.
There ain’t no S on the end…
No matter how many individual pieces there are, they are like fish, got it? Okay? There can be no S.
There may be lots of fish in the sea, or lots of lego on the floor.
There may be a school of fish, or a pile of lego.
You can catch some fish, or play with some lego.
You can add some fish to your aquarium, or add some lego to your collection.
You can scoop your fish into a net, or put your lego back into the box.
For, verily, The Lord hath spoken.
(And so have my parents, who told me 50 years ago to pick up my lego. Never did they utter an S And never shall I )
If corporations are people, then sure. To me, the question is, who really owns the word? The multinational corporation that trademarks it, or the people who use it in natural language?
The answer to me is clear. The word becomes dialect. No dialect is any better than any other.
This has nothing to do with corporate personhood, and everything to do with creation. The word is not dialect, it’s a proper noun, like a name.
Although I am a slight hypocrite about this, because I think calling a gif a “jif” is dumb.
Damn. I was just going to ask you how you pronounce “GIF”. (I happen to, by coincidence rather than knowledge, pronounce it as intended: jiff. My mind went to “gin” instead of “gift” when I first saw GIF, so pronounced with the English “j” sound.)
But, no, popular usage and local dialect also takes sway with proper nouns. You can’t steady the vicissitudes of language by dictating how to say a word or how to pluralize it or whatnot. EBay is spelled with a small “e,” and but at the beginning of a sentence many style guides say capitalize it. NASA is supposed to be in all caps, but British publications often write it as a normal proper noun, as Nasa.
And, regardless, Lego, I mean, LEGO (the LEGO name is always spelled in capital letters), is the name of the trademark, not the bricks. Those are LEGO bricks or LEGO interlocking bricks. So calling the bricks “Lego” is not any better than calling it “Legos.”
And straight from the horse’s mouth (PDF):
ALWAYS write the LEGO brand name in capital letters.
ALWAYS use a descriptive noun after the LEGO brand name, it must never appear on its own
E.g. wrong use: I play with LEGO.
E.G. correct use: I play with LEGO bricks.
It does go on to say, yes, not to add a plural “s” (not because it’s a quaint regionalism, but because you’re not supposed to use it as a noun referring to a LEGO bric)k, but you also can’t add a possessive s or even a hyphen to it.
So I hope you follow these rules, too, since, like you said, they’re from the actual owners of the word.
How do you pronounce the word “graphical”?
I don’t. I say “Lego piece” or “Lego set”. I don’t say “a Lego”. That would be as dumb as saying “Legos”
Probably as you do. But the constituent components of an acronym do not dictate how that acronym need be pronounced when spelled, of course.
Do you say stuff like “I like to play with Lego” or “Look at the house Johnny built of Lego” or something like that? No-no, according to the creators of the word.
Probably, when using it as a collective for whole sets or our entire collection of Lego. So yeah, not keeping exactly to their rules. But I (and everyone I know) used singular Lego before we ever knew there was a rule, or a controversy. It was always “Lego” even if used differently than the “rule”.
Which goes back to what I first posted.
Well, similarly, we (and everyone I know) always used the plural Legos before we knew there was a rule, or a controversy. It sounds off to our ears (as the reverse does to yours) to hear “Lego” as a mass/material/collective noun, or however you want to classify it. We think of “Lego” as the individual bricks themselves.
I don’t care one bit about what the makers of Lego want people to say, I’ve always heard multiple Lego blocks referred to as “Legos.” It sounds perfectly normal to me and that is what I will continue to say. “Pieces of Lego” sounds idiotic.
Wow, Brits and Americans use different words, who would have thought. 
Like I said earlier, I don’t see the corporation who trademarks a word as the “owner” of the word in any meaningful sense. I don’t mind when someone calls any soft drink a Coke, or when someone calls any tissue a Kleenex, or when someone suggests I Google headphones on Target’s website–even though the respective corporate “owners” of those words would absolutely mind.
Lego may have invented the word, but the word has passed into popular usage, and language doesn’t have owners.
I’ll call someone by the name they ask because it’s a sign of respect to them as a human. I don’t owe any such duty of respect to a corporation.
We agree exactly.
I agree as well.