That first statement is hard to agree with because it takes an all-or-nothing stance in a broad manner (must + little use). Most people will disagree because there is probably a "I don't 100% agree" reaction to it. You'd probably get the same reaction going in the opposite direction.

In our society everyone must work together to succeed. It is of little use to try and effect change alone as one person cannot make a difference in politics or work.

Meanwhile, the other two statements are much more direct on the stance being questioned. The examples are the only open ended part as interpretations can differ between people, but they are still clear enough to get the intended meaning across.