When Do Ideas Stop Having Objective Value?

1. It is a bad idea to swim off the coast of South Africa where the great white sharks hunt seals.
2. It is a good idea to get some exercise every day.
3. Islam may or may not be a good idea. We can't judge.
4. Christianity may or may not be a good idea. We can't judge.
5. Buddhism may or may not be a good idea. We can't judge.
6. Atheism may or may not be a good idea. We can't judge.
7. Nuclear families may or may not be a good idea. We can't judge.
8. Broken families may or may not be a good idea. We can't judge.
9. Sex outside of marriage may or may not be a good idea. We can't judge.

What characteristics must an idea have in order to be given a valuation relative to other ideas? The first two examples are individual acts that affect your health. However, that can't be it as #9 is as well. It can't be a matter of scale, because we know the following.

10. Nazism is a bad idea.
11. The Confederacy was a bad idea.
12. Racism is a bad idea.

Is it that we can only judge large-scale ideas if they belong to the past? No, because we have this.

13. North Korea's tyranny is a bad idea.
14. Al Qaeda is a bad idea.

Carrying this line of questioning out in my head, the only governing rule I can come up with is this.

An idea is bad if we say it is. We can judge an idea if we say we can.

How's that for objective, logical reasoning?

Note: I'd probably change #5. I doubt a poll of our elites from academia, the arts and politics would say anything but "Buddhism is a good idea," but that just makes my point again.