Theoretical Linguistics in the Generative tradition is entirely based on empirical data. If a theoretical linguist proposed a theory without any empirical data to support it, they would (and do) get laughed at.
The poverty of the stimulus argument (which can be traced back to Plato) has plenty of evidence supporting it. Yes there is negative evidence provided to children in some cultures. In North American elementary schools and often at home, children are told when they are saying something that is considered 'wrong'. There are many cultures, families and situations where this does not happen at all and children will learn their native language just by being exposed to people in their community using language. In that case the child is only exposed to positive evidence. What is crucial here is the fact that children CAN learn a language with only positive evidence. They just listen.
In addition, the similarities between the languages of the world far outweigh the differences. There is no way to account for this fact without positing some innate knowledge of language.
Also, read up on the distinction between competence and performance. I noticed you mentioned 'language use'. Yes, it is a mistake to base a theory on language use. We are talking about an ideal speaker-hearer situation. Language in a vacuum. Sound familiar?
Plato made plenty of bad arguments, too, and there are a lot of arguments that go back to his time. Anyone who is learning a language receives a constantly stream of feedback about how their communication is perceived, whether or not this feedback is explicit, modeled correct behavior, or delivered simply through incomprehension. Children are constantly deducing good and bad hypothetical "rules" all the time, and putting them to the grim and unforgiving test of trying to get people to understand them. Kids will happily overapply a general rule (like forming a past tense with "-ed" with a strong verb, "I readed it") even in the face of constant explicit negative input, but if they try a bad rule of syntax they'll get a string of gobbledygook that people don't understand and may even ask for clarification.
There are many, many fewer linguistic universals than some would have you believe, and many of these are best explained as similar tradeoffs between different needs, rather than a universal underlying pattern mysteriously encoded in the human mind.
The centrality of the distinction between linguistic competence and linguistic performance is exactly one of the bad premises of Chomskyan linguistics. The ideal speaker-hearer is as worthy a topic of scientific study as a unicorn: nothing more than a thought experiment. But then, Chomsky was not trying to describe the psychological reality of language use and language production, but rather articulate a formal system that could represent the structure of carefully curated and constructed phrases.
Humans are embodied, and they have things like working memories and perceptual metaphors. And human languages are not formal schemes of rules, but rather a complex and messy welter of social conventions.
You were almost coherent until you get to your assumptions about 'what people would have me believe' about linguistic universals. There are many universals that can be explained by generative grammar. There are numerous examples. 'tradeoffs between different needs' is not an actual argument. It is ridiculous that you are replacing 50 years of work with something so unscientific and vague.
I think you know damn well that there are patterns in the mind. They are posited for many things. Generative Linguists want to determine which of those patterns can account for certain linguistic phenomenon.
Physicists and Mathematicians study idealistic events, matter and object in idealistic spaces and conditions all the time. They don't study unicorns.
You cannot account for the fact that humans can instantly parse novel sentences using 'complex and messy social conventions'.
I cant tell you have no idea what Generative Linguists do and have never really read any of the literature. You (like a lot of people here) are just repeating the predictable things people say when Chomsky comes up that they probably overheard once.
It's certainly true that I've read more of Chomsky himself than the immense literature he spawned; and most of my reading of the generativist literature is at its messy edges where those explanations tend to be pretty unconvincing. Focus your reading on dubious generative accounts of morphologically-rich languages and it's easy to become disillusioned with the paradigm. "Principles and parameters" is where he lost me, but Chomsky himself has retreated from so many positions over the decades, when theory meets evidence, that it's hard to tell in a coherent way what his theoretical framework actually is anymore.
I'm not really "replacing 50 years of work" so much as speaking from a different paradigm. Linguistics is a discipline of multiple competing paradigms, and suffers the resulting problem of people talking past each other because they do not share the same premises or assumptions about the field of study. It's not my fault that Chomsky led a generation of linguists down so many blind alleys for decades. But I don't know how many people would defend something like "The Sound Pattern of English" over say, optimality theory.
I don't even agree that there are many linguistic "universals". Most so-called "universals" are rather implicational tendencies, which do not require appeals to native grammatical knowledge to explain. You don't need a "head branching parameter" to explain many head directionality tendencies, just the general human tendency to pay more attention to elements at the edges of statements and the process of diachronic systematization. True linguistic universals are very few, and frequently seem to me to be more general cognitive universals in linguistic disguise. https://www.princeton.edu/~adele/LIN_106:_UCB_files/Evans-Le...
Generative grammar itself does not attempt to explain the psychological reality of how living humans parse and process novel sentences, but rather to describe an abstract system of knowledge of a WEIRD and mono-lectual standard language known by ideal speaker-hearers (who lack such prosaic things as "memory limitations"). Idealizing language is one thing, but this idealization seems quite different from language as the semiotic practices, social conventions, and shared cognitive tools used for communication by multi-lectual human animals as a core element of their social behavior.
Also, read up on the distinction between competence and performance. I noticed you mentioned 'language use'. Yes, it is a mistake to base a theory on language use. We are talking about an ideal speaker-hearer situation. Language in a vacuum. Sound familiar?