"many reputable vitamin companies will sell supplements that combine magnesium with calcium even though the calcium will prevent absorption of the magnesium"

We already discussed this. Do you think the vitamin makers don't know that?

"Many places sell flax seed oil claiming it's got similar omega-3 benefits to fish oil, and it doesn't. "

Not exactly similar, but different. Is it better to eat a carrot or broccoli? Shall we debate that? Why not eat both? Fish oil can't provide ALA. How much EPA and DHA do we really need, and how efficiently is ALA converted to those? Many websites differ greatly on their opinion. I have admitted that taking both fish oil and flaxseed oil may be useful. Why can't you admit the same? I don't consider myself an expet on this topic, however I have read many websites recently on the flaxseed oil vs fish oil debate. Most articles lean one way or the other. A few do advise people to take both though. The argument for flaxseed oil is cost, the body's other uses of ALA besides making EPA and DHA, lignins present in high lignan flaxseed oil, and possible pollution or contamination(or rancidity) in fish oils. the argument for fish oil is that the conversion to EPA and DHA might not be that great, and some people might even lack the enzyme to do the conversion and not convert any. The flaxseed advocates say that people can eat fatty fish to get fish oils. Some people don't eat fish though. After my recent research into mercury in fish and the low levels I saw in salmon, sardines and herring, I am now not afraid to start eating those again. I like that idea better than taking fish oil supplements.

"Are you a vegetarian?"

I guess I would describe myself as a vegetarian who cheats?. I actually ate meat today, my first meat meal in over two months. I have not eaten fish in over two months, but plan to start eating fish again soon. I eat eggs, yogurt, and cottage cheese.
I think it is okay for people to eat meat as long as the animal is slaughtered humanely. My issue is that the average person in the US eats way too much meat. Perhaps many eat meat in over 10 meals a week. Limiting meat to less than 4 meals a week imo makes great sense.