Objective Grammar &c

 Moderns are egalitarian and will tell you that however a language is used is correct. As expected, egalitarians are full of shit. 

 Correct grammar is as simple as possible while allowing as much complexity as possible. If there are two alternatives, the more powerful one is more correct. There's also the consistency criterion, though that should go without saying. In theory you could have two equally powerful and consistent alternatives, but that never happens in practice. 

 Bad grammar makes the language gooshy and fuzzy. It means to say certain things you have to go out of your way to specify stuff that should be obvious from the grammar. This means anything that makes the language unnecessarily weak can be identified as bad grammar, regardless of how widespread the usage. 

 As usual I have difficulty with examples so I'm going to use vocabulary instead of grammar. Can you translate one hundred into a language which has numbers no higher than two? (1, 2, many.) Yes. It's merely a huge pain in the ass. It's two and two and two and two and two .... and two. Fifty times, specifically. Bad grammar bloats the language the same way. (P.S. Untranslateable is a meme. Maybe it happens in creoles, and then only sometimes.)

 Of course, bad grammar is fine if you're stupid and would never need a number as high as 100. If you're innumerate, this simply isn't a problem. Simple minds can rely on context because they never leave their home village and their context never varies. Reminder: average IQ 1800 was 115, and in Socratic Athens, 125. It is not surprising that 100 IQ grammar is shitty grammar.  

 Given an existing grammar, there is a Platonic ideal of that grammar, which is good grammar. Getting arbitrarily close to that grammar is not even impractical. (Idiots aside. It's fine to exclude folk who are too short for this ride.) 

 You can always compared Italian to Latin and notice that Italian has no advantages over Latin. It's simply worse - unless you think 'less taxing on morons' counts as an advantage. Italian is dumb-Latin. Ye olde scholars said languages 'corrupt' over time because that's the correct word to use for the evolutionary change. (They weren't politicized yet.)  

 Why does it matter that they use everyday when they mean every day? It means you can't easily distinguish between an everyday drink and an every day drink. Bullet coffee can't be called everyday even if you drink it every day. "You can tell from context," which means the opposite context is removed from consideration, and you have to add in a bunch of clauses if you want it back. Bad. Weak. 

 "We don't particularly need a word that means killing every 1 in 10." Unless you want to read the classics without confusing yourself. Or want to know what words mean so you can construct new ones. "Decimal sounds so violent, lol." If you want to say they were ravaged, shredded, or annihilated, try using words like [ravage] or [annihilated]. Or, kindly seek Canadian Healthcare. You owe it to yourself.

P.P.S. Efficiency is a sin. What 'we' [need] is an intricate and gloriously detailed language, which means having lots and lots of words we don't [need].

Though admittedly less Latin bureaucratese. It's called a bang, not an exclamation point. "Why use one syllable when five will do, lol." Don't be gross.