The world has not yet rallied to the cause of defeating aging. Aging remains by far the greatest cause of suffering, pain, and death in this world, and yet it is accepted as set in stone by the vast majority of people. Few think of doing something about it. Little funding goes towards the research and development programs that could plausibly bring aging under medical control, indefinitely extending healthy life spans. Humanity spends more on sports stadiums than it does on addressing the impending death and drawn out, painful decline of everyone presently alive.
All of this is why, even as our community grows and we achieve success in spurring the start of a rejuvenation biotechnology industry, we must continue to aggressively advocate for the cause of rejuvenation research. It is why it is important to stand up and speak out, to argue in public, to make presentations and educate those who do not yet know that aging could be ended, if only sufficient resources were dedicated to that goal. Tools to aid in that work of advocacy and persuasion are always greatly appreciated - such as this long list of logical fallacies with specific examples for our field.
Alleged certainty: this fallacy consists of concluding something is true because "everybody knows" it is. "Everybody knows" that there are too many people on this planet and therefore rejuvenation is a bad idea; "everybody knows" that life-saving treatments, such as rejuvenation, will always be only for the rich; and so on. Whether or not everybody actually knows these things doesn't matter; what does matter is the evidence used to back them up. For example, overpopulation is not at all a black-and-white issue; whether we're overpopulated depends on the metrics that are taken into account. The best way to counter this fallacy may be simply asking for evidence and pointing out that simply claiming that everyone knows something isn't sufficient proof, especially if the topic is not at all uncontroversial.
Appeal to anger: this fallacy attempts to justify an argument based solely on negative emotions. In the context of life extension, this fallacy is rarely committed alone; it usually hinges on other fallacies or weak arguments that are used as premises. For example, someone might be outraged that you worry about life extension when, allegedly, there are much worse problems than aging in the world, and he might use the supposed outrageousness of life extension to gloss over the fact that aging is a problem, whether or not worse problems than it exist. If someone commits this fallacy, you should kindly point out that the way he feels about a statement or an idea is not what makes it true or false. Whether we're outraged by something doesn't mean that we can discount it.
Appeal to authority: the infamous appeal to authority involves believing a claim solely because the person who made it is in a position of authority or prestige. When discussing rejuvenation, the appeal to authority fallacy is sometimes observed when people say that rejuvenation isn't possible or that some possible negative consequences of it are certain because an expert said so. The expert in question might well be right, but in order to establish it, his evidence must be examined to make sure that he isn't genuinely mistaken or doesn't have some other reason to make an unsubstantiated claim. Explain that everyone can make a mistake, no matter how smart, authoritative, or knowledgeable he may be. You don't take for granted what Albert Einstein said because he was one of the greatest physicists of all time; his claims, too, need proof, and until said proof is presented and verified, you can't say whether the claim is true or false.
Appeal to motive: this fallacy consists of dismissing an idea on the grounds of the motives of its proponent. A typical life extension-related example is that of patient-funded clinical trials. At such an early stage, experimental rejuvenation therapies are indeed expensive, and governments may not be willing to pay for what seems like a moon shot. Thus, wealthy people willing to pay to try the therapies are effectively making it easier to test them. Some people may argue that wealthy people are doing this not to help the research but for their own benefit; consequently, they feel outraged and despise the idea of patient-funded trials entirely, deeming it nothing but proof that rejuvenation is only for the rich. Explain that anyone's motives for endorsing an idea are irrelevant when assessing whether the idea is good or not. It may help if you explain that you too disagree with the motives of people who push life extension only for their own interest but that life extension is a worthy goal per se.
Appeal to nature: the appeal to nature fallacy consists of implying that everything that is natural is better than everything that is not natural. In the context of life extension, you can expect to encounter this fallacy as the most classical of objections, the one and only "but aging is natural, while rejuvenation is not!" This fallacy is why people infer that aging is better or more desirable than using rejuvenative therapies to avoid it-which is not unlike saying that having cancer is better than using immunotherapy to cure it. The appeal to nature fallacy is easily countered with examples of undesirable yet perfectly natural things that we suffer from and desirable yet unnatural things that we use every day. Depending on how entrenched someone is, you can expect that person to resort to a double standard right after - "yes, but with aging, it's different." It is not. The bottom line is that naturalness is not a sufficient criterion to judge whether or not is something is good or desirable, regardless of what that thing may be.