Why should Mandarin be the mother tongue of all Chinese?
It simply is not anyone's mother tongue. Even the Beijingers (originally non-Chinese town
)from whose dialect it derives from make fun of it. It was not even the mother tongue for the Manchu (non-Chinese people
) who created it. Rather it was a government-mandated idea to synchronize the language for convenience. A point of pride for Mandarin was when it was first created back before ww2, only 1 or 2 people could speak it properly.
A mother tongue is what your ancestors spoke. Your ancestors very likely did not speak Mandarin. It would've been a foreign language to them.
As you already mentioned, we learn other languages because we need to communicate. Knowing a mother tongue is not a need, but an indulgence. It is loyalty to your Chinese ancestors. You can say Mandarin is the national language now, but replacing your mother tongue with Mandarin is the simply disregarding the true nature of your Chinese ancestors.
Your ancestors spoke their languages (which the Singapore government calls dialects) for far longer than 90 years. Their lives, demeanour and entertainment are influenced by their languages and unique culture.
Of course if you believe that the Chinese should throw their 5000 years of history and culture in the garbage for a less than 100 year old foreigner invention that's up to you. But I find it ridiculous that you find a "Chinese language"
made by non-Chinese when they treated real Chinese like slaves to be a core belief for ancestor patriotism.
Really doesn't add up.