What's so fallacious about the Slippery Slope Fallacy?
When you look at the world, I think it's a rather non-controversial statement that a good percentage, if not a majority, of social problems are caused by people making choices based solely on short-term outcomes--"if X then Y, and Y is desirable, therefore I will do X"--without taking long term consequences into account. (ie. Y leads to Z, which is more undesirable than Y is desirable, therefore you should not do X.) But in a recent discussion with a friend that got into this territory, when I tried to point out undesirable long-term consequences, he accused me of employing the Slippery Slope Fallacy and declared my reasoning to be therefore invalid, and that was the end of that. And it made me wonder. Why is it formally considered a fallacy to try to reason beyond a single degree of cause and effect, and why does this explicitly only apply when reaching a negative consequence? (I distinctly remember, when we learned about fallacies in high school, that "X leads to Y, which leads to Z, and Z is desirable, therefore you should do X" is *not* considered an example of the fallacy.) It seems just a little bit Orwellian to see the name of Logic invoked to formally dissuade people from one of the highest and most practical forms of logical reasoning, namely reasoning about the long-term consequences of one's own actions. So what am I missing? Why is this considered a fallacy?