Straw man. This is the fallacy of refuting a caricatured or extreme version of somebody's argument, rather than the actual argument they've made. Often this fallacy involves putting words into somebody's mouth by saying they've made arguments they haven't actually made, in which case the straw man argument is a veiled version of argumentum ad logicam. One example of a straw man argument would be to say, "Mr. Jones thinks that capitalism is good because everybody earns whatever wealth they have, but this is clearly false because many people just inherit their fortunes," when in fact Mr. Jones had not made the "earnings" argument and had instead argued, say, that capitalism gives most people an incentive to work and save. The fact that some arguments made for a policy are wrong does not imply that the policy itself is wrong.
In debate, strategic use of a straw man can be very effective. A carefully constructed straw man can sometimes entice an unsuspecting opponent into defending a silly argument that he would not have tried to defend otherwise. But this strategy only works if the straw man is not too different from the arguments your opponent has actually made, because a really outrageous straw man will be recognized as just that. The best straw man is not, in fact, a fallacy at all, but simply a logical extension or amplification of an argument your opponent has made.
Slippery slope. A slippery slope argument is not always a fallacy. A slippery slope fallacy is an argument that says adopting one policy or taking one action will lead to a series of other policies or actions also being taken, without showing a causal connection between the advocated policy and the consequent policies. A popular example of the slippery slope fallacy is, "If we legalize marijuana, the next thing you know we'll legalize heroin, LSD, and crack cocaine." This slippery slope is a form of non sequitur, because no reason has been provided for why legalization of one thing leads to legalization of another. Tobacco and alcohol are currently legal, and yet other drugs have somehow remained illegal.
There are a variety of ways to turn a slippery slope fallacy into a valid (or at least plausible) argument. All you need to do is provide some reason why the adoption of one policy will lead to the adoption of another. For example, you could argue that legalizing marijuana would cause more people to consider the use of mind-altering drugs acceptable, and those people will support more permissive drug policies across the board. An alternative to the slippery slope argument is simply to point out that the principles espoused by your opposition imply the acceptability of certain other policies, so if we don't like those other policies, we should question whether we really buy those principles. For instance, if the proposing team argued for legalizing marijuana by saying, "individuals should be able to do whatever they want with their own bodies," the opposition could point out that that principle would also justify legalizing a variety of other drugs -- so if we don't support legalizing other drugs, then maybe we don't really believe in that principle.
http://www.csun.edu/~dgw61315/fallacies.html#Slippery%20slope">Logical Fallacies and the Art of Debate