This is the most wonderful time of the four-year span for logicians. I am not a logician, but I love advocating for logic. People hate me for always wanting a reason, but even more so for constantly asking, "What exactly do you mean by that?" which is the main weapon for a student of philosophy.
This brings me to the fallacy I hear most and which I consider the most ridiculous: the slippery slope.
The main context in which it is used against me in an argument is in regards to my secular tendencies. The claim is that without religion, there would be no morality, and the world would degenerate into anarchy. One problem with that is that the theist definition of morality and what morals are most important is usually quite different from the construction of humanist morality. The Ten Commandments are a great example, since all of the Commandments are considered highly important.
1) I am the Lord thy God, who brought thee out of the land of Egypt, out of the house of slavery.
2) Thou shalt have no other gods before Me. Thou shalt not make unto thee a graven image, nor any manner of likeness, of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth; Thou shalt not bow down unto them, nor serve them; for I the Lord thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate Me; And showing mercy unto the thousandth generation of them that love Me and keep My commandments.
3) Thou shalt not take the name of the Lord thy God in vain; for the Lord will not hold him guiltless that taketh His name in vain.
4) Remember the Sabbath day to keep it holy. Six days shalt thou labour, and do all thy work. But the seventh day is the Sabbath in honour of the Lord thy God; on it thou shalt not do any work, neither thou, nor thy son, nor thy daughter, thy manservant nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates; For in six days the Lord made the heavens and the earth, the sea, and all that is in them, and rested on the seventh day; therefore the Lord blessed the Sabbath day, and hallowed it.
5) Honour thy father and thy mother; in order that thy days may be prolonged upon the land which the Lord thy God giveth thee.
6) Thou shalt not kill.
7) Thou shalt not commit adultery.
8) Thou shalt not steal.
9) Thou shalt not bear false witness against thy neighbor
10) Thou shalt not covet thy neighbour's house; thou shalt not covet thy neighbour's wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbour's.
So, essentially, the Judeo-Christian theist perspective is that worshiping something besides the Hebrew God, creating art that depicts living creatures, cursing, working on Sunday, dishonoring your parents, murdering, cheating on a spouse, stealing, lying, and being jealous are all on the same plane of badness. Leaving aside the fact that most Christians violate at least one of these, I really can't believe that worshiping a non Judeo-Christian god, creating art, cursing, working on Sunday, or thinking jealous thoughts are truly crimes. Besides, how would the last one be regulated? Additionally, I don't think that adultery and murder are really on the same plane of evil, and American law is on my side, as adultery cannot be prosecuted.
More simply stated: the vast majority of the world's population claims to be religious, and yet not only does man-made evil exist, but certain reprehensible acts are committed using religion as a justification. Secularism only causes immorality if you define immorality via dogmatic instead of rational means.
Another example of the slippery-slope model is one argument that has been adapted by homophobes. Some claim that without religious injunctions against homosexuality, the human race would die out because everyone would "turn gay" and would no longer participate in procreative sex acts. Three simple facts call this assertion into question: the world is overpopulated as it is, modern heterosexuals can live non-procreative yet sexually fulfilled lives, and some LGBTQ community members engage in occasional procreative acts (or turn to artificial insemination) in order to have children. The funniest part of such an argument, to me, is that it would suggest that every person, or at least a majority of people, would "turn gay" if loosed from religious bonds. I love asking people who use this argument if they would "turn gay" if they weren't religious, as they tend to flounder or avoid the question with a great measure of awkwardness.
Some more slippery slopes that aren't accurate:
- Having sex at a young age leads to other socially deviant behavior.
- Marijuana use necessarily leads to the use of harder and harder drugs.
- Legalizing euthanasia would lead to the disenfranchised seeking out death.
The steepest street in the world (Baldwin Street, Dunedin, New Zealand)
It has a grade of 35%. Impressive, no?