I think it's quite dangerous how we can place ourself in pitfalls solely because the decision is in the eye of the beholder. If language acquisition (like another commenter rightfully said) were remotely the same as other processes, maybe the comparisons would be more apt. However, what exactly is wrong with making errors in the target language? Consider conversely this, is there actually a need for someone to arguably overlearn a language to a point (like many of us here) that we not only take for granted, but possibly entrap ourselves within a sociolinguistic framework?

The idea that we cannot learn a second language past 2x can be disproven, if there is evidence for it - there is no law here. More importantly, as that is not an interesting question - why might it be the case that we can't? To be frank, it might just be because you are telling yourself the lie that you couldn't, because of the investment you've made in your native language.

"Errors" in a second language are arguably not always such a bad thing - yes, communication is important but does overlearning one language prevent us from making more progress in others? Also, if we stop considering errors to be a bad thing, then we face the potential reality that novelty is present everywhere in second-language learning, but when speaking your native language the experience of novelty (in relation to the language) is nigh inexperienced. Except, in many cases, when someone speaks "improperly" or wrongly.

We cannot as a culture distinguish ourselves from the desire for everyone to be like us, and/or for ourselves to be like everyone. Of course someone will come along and disagree, but my point on that note is that perhaps the significance of the errors we attach related to language is simply code for our disdain for something else.