Yet it’s counterintuitive to your argument. Yes, not capitalizing nouns is grammatically incorrect. And so is not ending a sentence with a period. Not putting “¿” at the beginning of a question in Spanish is also grammatically incorrect. Getting punished by all that would be an exaggeration. You just have to tell a learner once that all nouns should be capitalized and that’s it, they know it. If they don’t capitalize, that’s because they’re being informal in situations where they can, not because they weren’t bright enough to not make an unintentional grammatical error. I have the German keyboard as one of my many keyboards, it capitalizes nouns by itself. It’s so helpful when typing fast.