In the answers and comments of this site there are some recurring kinds of reasoning that I am afraid are misconceptions about what language is and how it is studied. I believe it would be useful to clarify some points, not to have to address them again and again.
The word XXX is ugly Opinions are often offered about the fact that a word or a phrase “is ugly”, “sounds bad”, “is cacophonous” and the like. Now, while the experience of a native speaker of a language is invaluable, not every personal taste is an addition to a discussion about a linguistic phenomenon. Rather, in general such remarks are no more interesting than “I like coffee” or “I dislike jazz” and no especially useful when attempting a scientific discussion of language.
I never heard/always hear XXX This is a bit better than the previous case, but I'd confine such remarks strictly to comments, since it is not always clear whether they reflect a comprehensive understanding of language or an accident of the writer's idiolect. And I'm saying so for myself first: I am not exactly a child, but I still learn that some words or linguistic uses are especially frequent or especially rare in my town / circle of acquaintances / texts I read, and so not representative of Italian in general.
The dictionary says so! This is a rather subtle point, and in a sense the opposite of the previous ones. We all agree that reliable sources are of the utmost importance, so when we are discussing lexicon there is no better source than good, authoritative dictionaries (for instance Battaglia, Treccani, Zingarelli, De Mauro, Devoto-Oli, Sabatini-Coletti, rather than anonymous, web-based ones; and Battisti-Alessio or Cortelazzo-Zolli for etymology).
But it is important to understand what dictionaries actually are, since it seems that some people have some misconceptions about this. Dictionaries are not prescriptive authorities, they do not fix what can or cannot be written and said. They register the use of present and past speakers, and even that they don't do in real time.
In a Crusca linguist's words to a schoolboy:
È così che funziona: non sono gli studiosi, quelli che fanno i vocabolari, a decidere quali parole nuove sono belle o brutte, utili o inutili. Quando una parola nuova è sulla bocca di tutti (o di tanti), allora lo studioso capisce che quella parola è diventata una parola come le altre e la mette nel vocabolario.
(It works like this: it's not scholars, those who make dictionaries, that decide which new words are good or bad, useful or useless. When a new word is used by all (or many) people, then the scholar understands that the word has become a word like all the other ones and puts it in the dictionary.) [My translation]
Many people say so! The simple fact than many people say or write * metereologico rather than meteorologico, * non c'è ne sono rather than non ce ne sono, * colluttorio rather than collutorio, * se io sarei rather than se io fossi, and so on, does not make these forms immediately and universally part of standard Italian. They have to become so widespread as to become (and be perceived as) a new norm, but since many other people feel these forms to be incorrect, they effectively are.
It is true that many single words and grammatical constructions began as “errors” (crollare used to mean “to oscillate”, not “to fall down”; after a negation one was supposed to use alcuno rather than nessuno; bistecca was a weird adaptation of “beefsteak” and so on), and in a sense the whole of Italian is a “wrong” form of Latin, where everybody ignores the use of declensions and most Latin grammar, but it imposed itself as a new norm. It was a new, correct, vital language when most people began using it for everything from haggling at the market to writing love poetry. When metereologia and se io farei will be analogously widespread, they will be de facto correct. Now, they aren't.