Strike the word 'easily' from your first sentence and I agree with you wholeheartedly.
Was about to say the same. You do have to worry a little more with plant/legume based proteins about mixing and matching complementary proteins to make sure you're getting all the essential amino acids that you'd otherwise get from a serving of meat, which is considered a complete protein. That said, it's still relatively easy to do. On that note, re snoodog's comment- suggesting that we're not good at converting animal protein to useable energy/nutrients, and thus should consume more animal protein, is flat out wrong. If anything, we should be eating way less animal protein than we currently do in the west, given that we're more equipped to derive sufficient protein and nutrients from small amounts of meat without taking on the risks related to high fat/cholesterol intake that come with consuming large portions of the same. Last I checked, there have also been a series of studies linking high intake of certain meats with increased risk of certain cancers. Think red meat is still linked to gut cancers, and a recent study suggested that consuming a given amount of processed meat (eg bacon, sausage, salami, baloney, etc) presents a cancer risk akin to smoking cigarettes. Discard the environmental argument if you will (although I don't really understand why you would), but don't assume that more meat = better lifestyle. Current data doesn't support it, and basic nutrition supports the opposite.