I have been a vegetarian for many years. I 'sin' now and then, so I'm not that strict.
Strangely, the reason why I eat meat sometimes, is because of it's price. I'm not exactly rich. For me, to stay healthy as a vegetarian, I need to eat varied. Yet a lot of the good 'replacement' stuff is quite expensive in Holland. Meat, on the other hand, is heavily subsidized by the government.
Main reason for me to choose not to eat meat, has been mentioned before: Waste of rescource.
Too much land is used for herding instead of farming. What's worse, every day still, tropical forest are being cut down to make way for big cattle ranches.
On the other hand, there is a similar problem with soy-products. For soy, a lot of rainforest is being cut down, and what's worse, over-fertilizing of the created farms (because rainforest soil is very, very poor soil; rainforest thrives on itself) causes the nutrients to wash into the sea, causing massive damage to coastal ecosystems.
But then, consider that most of the soy produced is used for making food for cattle, and not for feeding the vegetarians around the world.
As for milk; It is true that scandinavian people, and people in western Europe in general, have a recent (say, like 20.000 year) mutation that enables them to endure milk. I say: endure.
It still does not mean that we are fully capable of digesting milk properly. It only means that we have less cases of lactose sensitivity among the population, then, say, Asian or African countries.
I think that eating meat or drinking milk is not automatically bad for your health.
But the tendency to eat meat and drink milk every day, I'd say, is not healthy.
Gruesome fact: All Herbivores have 7 meters of colon lenght. All Carnivores only have 2 meters.
Why? Even in your stomach, and in your colon, meat keeps decomposing (rotting). Most bacteria involved in that process are resistant to our acid's stomach and most enzymes involved in digestion. Meat needs to be digested and excreted quickly...