But we need these alphabets to allow people of various culture to be able to have url in their native language, and I'm not sure how browser could help disambiguate all the possible Unicode symbol, afaik while there are some font to make each symbol as distinct as possible (I think they are used in licence plate), none of them support all of Unicode.

Also, while I can agree that url are "security-critical", the same applies to email or even just names, and we definitely need Unicode for those.