While my computer was down I read an article by Jim Daly on why gay marriage is a bad idea. Jim Daly is the President of Focus on the Family. You can read his article here. http://www.focusonlinecommunities.com/blogs/Finding_Home/2011/05/24/why-same-sex-marriage-will-fail I found his arguments to be so poor that if I wasn't already certain that gay marriage is bad I would be convinced it's a good idea. So that vein here are four general guidelines to making an effective argument.
1. Be as consistent, honest, and reasonable as you can. Inconsistency is not just a sign of hypocrisy, it's a guarantee of a bad argument. If you're not honest no one should listen to you. You can demand that someone account for every logically possible explanation for X, but this is quite unreasonable as there are a lot of highly improbable but logically possible explanations for X. If you demand that every possible explanation is ruled out (or in) than nothing can get accomplished as it is nearly impossible for anyone to meet that demand.
2. If you use any evidence, statistics, or premises that are not obvious or are controversial, make certain you cite the sources or prove the premise. You don't have to cite a mathematician if you claim that 2+2=4, as that is obvious to everyone who knows math. However if you are talking about theoretical calculus than citing a mathematician or proving the premise is necessary.
3. Make sure you use good logic and reason and don't use any logical fallacies. A lot of "common sense" is logically fallacious. The most common example is that most people do believe that correlation establishs causation. It doesn't.
4. Keep your argument as simple and easy to follow as possible. Don't start arguing for socialized health care and wind up "proving" that people are basically evil. Some problems and issues are quite complicated and it can be difficult to keep them simple. The process oil goes through from extraction to fuel for a car is logistically very complicated. If an "argument" is tracing this process it will get long and quite complicated. But even here if the process is explained well enough it will be easy to follow. Doing this will make your argument stronger and enable you to communicate with people better.
There are other guidelines that can help, but following these ones should keep you in good shape.
How do Daly's arguments shape up? Well pretty poorly. The only one of these criteria Daly meets is part of the first one. Daly is honest, but every other aspect of his argument(s) is terrible. Nothing he says is convincing because his argument(s) is fallacious, unreasonable, needlessly complicated, and he doesn't cite anything.
It's not clear if Daly is giving one argument or several because his article lacks a clear thesis (a single statement summarizing his main point) and the organization of his article is poor. He says he can argue against same sex marriage, "On the basis of logic, reason, common sense and the fact that preservation of traditional marriage is in the best interest of the common good, as evidenced by any number of factors, including reams of social science data and thousands of years of history." But then he jumps all over the map. He discusses things that seem to have no relation to gay marriage (abortion) and ends up arguing that gay marriage advocates are infringing on religious rights (Which may be true, but it in no way establishes that gay marriage is a bad idea; it establishes that proponents of the idea have behaved badly).
Daly doesn't cite a single source for any of his evidence or premises. He is arguing from social science statistics (which are vague and often misleading under the best of circumstances) but he doesn't say where he is getting his evidence. I don't think he is making them up, but without the citations I can't know that, and I can't check the evidence to make sure it is accurate (perhaps the social scientists Daly got his information from used bad methodology?).
Daly's argument(s) are fallacious because the actual arguments he gives have little or nothing to do with gay marriage. Whether previous social and cultural changes had good or bad results doesn't establish that gay marriage will have a good or bad result. Each cultural change must be judged on it's on merits (or lack there of) not the fact that other changes had bad results.
Daly doesn't even effectively argue that these other changes had negative effects. Don't misunderstand, I stand with him in affirming that things like abortion and cohabitation are morally wrong. However he's trying to argue that such things have directly lead to certain social ills, but he's using a common logical fallacy. He's assuming that correlation does establish causation, and it doesn't. The fact that cohabitation and child abuse increased at the same time doesn't establish a causation between the two. Maybe it's the other way around and child abuse caused the increase in cohabitation?
I am quite convinced that gay marriage is a bad idea and is morally wrong, but nothing Daly said in the article effectively argues that fact. Part of the reason I decided to critique Daly is that I affirm his conclusion, but the way he got there is just terrible. It is important to critique people you agree with when they use bad arguments and reasoning. One of the primary problems with most ideological and political groups in America is failure to be self critical.
So don't argue like Daly. Make every effort to keep your arguments reasonable, consistent, logical, simple, and always cite your evidence (when appropriate). Otherwise you'll be acting like a congressman or a fool.