"50% of people are unintelligent" or "50% of the people are unintelligent"?

Question

My First Question:

As far as I know, after the phrases like "many of", "some of" and "all of", we can't use a noun without the article. For instance, we cannot say:

"All of people are unintelligent"

We have to say:

"All of the people are unintelligent"

to use the phrase "all of" even if we are talking about all people who are alive. Am I right?

Can I say "All of the people", "Many of the men", "Some of the women", etc, if I am talking about all people in the world, many men among all men in the world and some women among all women in the world etc.?

I know that I can say "All men", "Some people", etc without using the word "of" by the way, but I wonder if I can say those phrases like "all of the" instead.

I also know that I can use those phrases which include the phrase "of the" when I talk about a specific group of things like in:

All of the players of the American team are very athletic.

Here I am referring to the players in the American national basketball team while watching a game.

But, as I said I want to know if can use those phrases which include "of the" for referring to things generally. I mean, when I talk about all basketball players in the world instead of all basketball players in the American team, can I say:

All of the basketball players are very athletic.

My second question:

What about the sentences where we use percentages? If I am talking about all people in the world generally, can I say:

50% of people are unintelligent.

Or do I have to say:

50% of the people are unintelligent

Answer 1

For your first question: The word 'of' is these cases is being used as a partitive; it's used to connect some quantitative description to a group or collective noun, to specify a certain subset. This is also commonly used for counting numbers of a particular set, e.g.:

Six of my students got 100% on the exam.

Four of his friends went to the party.

The linguistics here are beyond me, but in English at least, the group after the noun has to be a specific group, so you cannot say 'all of the people' to mean everyone generally. 'The people' in this phrase will always be interpreted as some specific group of people. Similarly, 'all of the basketball players' will always sound like you are talking about some specific group of basketball players, not basketball players generally. If you said

All of the people are unintelligent

in a conversation without ever specifying what group 'the people' refers to, the listener won't be sure what group of people you're referring to. If I heard that sentence, I wouldn't think it meant all people generally, I would assume that I was missing some of the context.

For your second question: Grammatically, I believe this is the difference between a partitive and a quantitative. When you way

Fifty percent of the people

'of' is again a partitive, so it's functioning to describe a subset of some particular set. In this phrase, 'the people' ought to be interpreted as some particular group of people, just like in 'all of the people'. When you say

Fifty percent of people

'of' functions as a quantitative. Here, the phrase 'fifty percent of' is specifying a quantity: how many people you are referring to. You can't say 'all of people' because 'all' isn't a quantity.

Answer 2

First answer

No, but you can say, "All basketball players are very athletic", "Many men", and "Some women", if speaking generally. You can also say, in the "all" case: "Basketball players are very athletic".

Second answer

You have to say "Fifty percent of all people are intelligent, and fifty percent are clever." Or, "Fifty percent of people like apples."

Details

When speaking generally about everyone, the expression "(quantity adjective like all, many, some) people" can be used. "(Percentage) of people" can be used, too. In the "all" case, "all" can be omitted.

When speaking about everybody in a subset of everybody, the expression "(quantity noun like all, many, some, a percentage) of the (group of people)" is used. Optionally, in the "all" case, "all of" can be omitted.