"Đạo đức là nền tảng vững chắc của con người."

Translation: Morality is the solid foundation of man.

[Amanesse77]

I think ''humanity'' should be accepted.

[Huy_Ngo]

It should be "human" or "humanity" instead of "man", because "man" is usually used to refer to a specific human and usually male.

[TehVanarch]

Nah, "man" is just a more archaic/older-fashioned way of saying "human" or "humanity" depending on the situation. "Man" is of Germanic origin while "human" and "humanity" are from Latin via French.

"Men" carries a stronger association with males than "man" (which oftentimes is used poetically to refer to humans).

Sometimes people get upset over misunderstandings like how the word "man" in spokesman just means a person or human but they've come up with spokeswoman to "avoid sexism".

[Huy_Ngo]

That's why I said "usually". As the word is archaic, it is used less at the present.

[TehVanarch]

It's still used a fair bit in biology papers, religious and philosophical works. As the sentence in question is one that relates to morality, using "man" is perfectly acceptable and I'd say a tad better sounding.