I encountered this logical fallacy while grading position papers today:
Because the U.S. has been compared to the Roman Empire, and because the Roman Empire fell, it therefore follows that the U.S. will fall just as Rome did.
It was my duty to correct the student with the following (excerpted) comment:
Magic Johnson, the famous basketball player for the L.A. Lakers, got H.I.V. and ended up with full-blown A.I.D.S. Another basketball player (we’ll call him Tony) has been compared to Magic Johnson, particularly because he is known to frequently practice un-safe sex. Therefore, because Tony has been compared to Magic Johnson, Tony will also acquire H.I.V. and end up with full-blown A.I.D.S.
This does not hold water.