I've got some time to look over Blacknad's list now and I can quickly dismiss the first two:
1 The placebo effect
2 The horizon problem
The placebo effect is well documented medically and surprises no one in medicine. The horizon problem really does not exist in physics if one accepts that inflation took place which nearly everyone does.
3. Ultra-energetic cosmic rays
I will grant there are likely a few exceptions to the rule not yet accounted for but this problem appears to no longer exist now that we more fully understand the affect of super novae shock waves and magnetic fields.
4. Homeopathy.
See #1. It is pure unadulterated nonsense.
5. Dark Matter
Dark matter is different from what was described in my earlier post. Dark matter seems almost undoubtedly to be axions.
6. Viking Methane
Of course there's life there. It is a planet isn't it? Every planet we have ever visited has life on it so why should Mars be any different? <g>
7. Tetraneutrons.
I'm totally clueless. I hope it is something really weird as that will help spur new research.
8. Pioneer Anomaly
See my answer to #7.
9. Dark Energy
This is what my previous article was discussing. I think it will just come down to being an intrinsic property of space-time. Which is very exciting.
10. Kuiper Cliff
Why not another planet? Or for that matter a failed star. And if not there now ... perhaps there in the past but swept away by a close encounter with another star.
11. Wow Signal
I hope it was an intelligent life form.
12. Not so constant constants
I can't believe anyone truly believes any of the constants are. That is just to comforting and things that are comforting to humans are always wrong. Perhaps Pi but I wouldn't even bet on that.
13. Cold Fusion
Bring me a bottle of Chimay. Hope springs eternal in those that want something for nothing.
The reason it is nonsense has nothing to do with "accepted theory." It has to do with the fact that you just can't fuse deuterium, or anything else, and not get gobs of perfectly obvious neutrons.
