There are many controversies in science, but most of them have a "right answer". Why should something which has a "right answer" be controversial? Well, it may be because people are simply ignorant of the facts or motivated by competing interests, or it may be that even though there is a right answer out there somewhere, we don't actually know what it is.
A good example of the first kind of controversy is the question of whether passive smoking (otherwise known as secondhand smoke or environmental tobacco smoke) is harmful. It is. It increases the risk of both heart disease and lung cancer. We know that passive smoking is harmful because extensive studies have been done, and have given a clear answer. It is also thoroughly biologically plausible, given that we already know tobacco smoke is harmful. There is no meaningful scientific doubt about those results. Nonetheless, it remains controversial, partly because tobacco companies spend a lot of money on PR to try to make people think that passive smoking isn't harmful, and partly because smokers don't like the idea that their habit is harming other people and may use denial as a mechanism for coping with the resulting cognitive dissonance.
Another example is the idea that vaccines cause autism (anti-vaccinationists don't really seem to care whether it's thiomersal-containing vaccines or MMR that causes autism, even though it would have to be the most spectacular coincidence in the whole history of spectacular coincidences if they were both to cause autism, presumably via completely different mechanisms). Anti-vaccinationists believe that vaccines cause autism because they are ignorant or even deluded. We know that vaccines don't cause autism because a huge amount of research has shown that they don't. So again, there is a right answer.
Man-made climate change is an interesting example of both types of controversy. We know that man-made climate change is a real phenomenon, although some people dispute this, again because of PR by industries with an interest in continuing CO2 emissions and cognitive dissonance among people with polluting lifestyles.
But we don't really know with any certainty exactly what the effects of climate change will be. How much will global temperatures rise? How much will sea-levels rise? Which parts of the world will get warmer, and which will have more severe winters? The answers to those questions are controversial simply because the science isn't sufficiently advanced to tell us the answer. There is a "right answer" out there somewhere, which we will discover in due course (probably the hard way), but right now we really don't know what the right answer is.
I was thinking about a story of another controversy I heard about on the radio this morning, namely water fluoridation, and it struck me that this is a bit different from most scientific controversies. In this case, I don't think there is a right answer.
Now, some people may tell you that water fluoridation is ineffective. They are wrong, much like those who tell you that vaccines cause autism or that Santa Claus exists. Much research has been done, and although individual studies are generally of poor quality, the amount of research and consistency of results is pretty convincing when taken as a whole: fluoridation of public water supplies leads to significant gains in dental health for the affected populations.
It also seems clear from that research that there are no major harms from fluoridation, but there is a small amount of minor harm in the form of dental fluorosis. This really is only a small amount of harm, leading to slight cosmetic imperfections in teeth in a small number of people.
But this is where it gets tricky. Given that the benefits greatly outweigh the harms, but that a small number of people will suffer a small amount of harm, is it right to fluoridate public water supplies? If you believe that interventions that do more good than harm at the population level are justified, you would say it is. If, on the other hand, you believe that fluoridation amounts to a medical intervention imposed on people without their consent (and which, remember, carries a small risk of a small amount of harm), then you could legitimately argue that fluoridation of public water supplies is unethical.
I really don't think there is a right answer here, or at least not one that science can provide. The right answer, if there is one, can only be found by philosophers and ethicists.