I agree it seems like a silly thing to do (block browsers without a valid reason, of which there are very few), but to blame JavaScript or modern web developmen

I agree it seems like a silly thing to do (block browsers without a valid reason, of which there are very few), but to blame JavaScript or modern web development in general is ridiculous. The user agent string is not a JavaScript concept. There may be some legitimate concerns about the modern state of web development (though I'd argue it's a positive thing on balance) but you've certainly added nothing new or worthwhile to that discussion. Your attitude is incredibly counterproductive, toxic even. And you're not doing yourself nor anyone else any favors. Put simply you need to get over yourself.