What Is Man's Greatest Enemy? Weakness?

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Personally, I beleive that man's greatest weakness and enemy is ourselves. Our greatest weakness is that, for the most part, we care about number one above all else. We would much rather help just ourselves than help the entirety of the human race. This in itself, makes us our own greatest enemy. And if that were not enough, it is because of man that our environment is so screwed up. Trash strewn everywhere, huge mother-trucking landfills, nuclear waste, greenhouse gases. All of these factors that have affected our environment have come to be because of humans. What's your take on this?