When forming an opinion people should do certain things.
1) Leave opinions at the door.
This tends to be a problem for most people. If you start by taking a side, then you are less likely to be open to new opinions.
2) Consider both sides.
Not just by listening to what both sides have to say but by putting yourself in their shoes. Remember, the people on both sides tend to have the same intelligence so don't discard one because you feel they are less intelligent. If you can not understand where they are coming from that means you still don't understand their side. Obviously both side have reasons why their side is right, so you must completely understand both. Do Not, assume that the most popular or politically correct side is right.
3) Reduce the pile of information.
If you weigh evidence based on how bias the source is, you will be able to reduce any faulty information. This includes the side you may have leaned toward before.
4) Examine the remaining evidence. Though both sides may still have relevant evidence, you can weigh this evidence as to how strong it is.
5) Consider both could be wrong.
Many times, the answer is not A, B, or even C.
6) Consider both sides could be right. Though this is not as common, it does happen.
7) Take a step back. Often times, if we focus too much on certain things, we fail to see the big picture. Some times, we even have to forget the topic completely. Ever been so focused on something like a persons name, but only remembered it when you stopped? Sometimes, an answer comes the moment you stop asking it.
Eventually, by using these steps, you can come to either a logical conclusion or at least be on the side that is most likely correct. You may have to add more steps depending on the topic.
This has benefits either way.
If you can conclude something, then you can prove to others you are right. You can also explain how your opponent is wrong.
If you have not made a conclusion, but only formed a more relevant opinion then you are at least less likely to be wrong.
By putting yourself in their shoes, you will become familiar with the oppositions side. This way you are more likely to have posed their question to yourself and already know how to defeat it.
As a note: Sometimes I like to take the oppositions side. Often times, both sides have people who make silly comments that just have to be addressed. By forcing them to think more about their side, you are actually making your side stronger. If you actually believe "yes" is the right answer but say "no" and give a strong argument. This forces people on the "yes" side to think more to defeat you. I would rather have people who think on my side than people that guess.
Determine what is considered practical and unpractical - as opposed to right or wrong. If any other type of species other than humans would've evolved to become the intellectually dominant species of the planet, their morals might - and that's a huge might given that a whole another environment than that of Earth is necessary to support my argument, then again its only a thought experiment - be different from ours. How we develop our societies and its regulations are deeply linked to how we can operate in our limited range of other people and environments.
Given that our cultural development has been vastly refined since, for example 50 - 10.000 BC to the present, just goes to show that we needed time to make sense of the previously unknown and find systems that benefited most in a society. So, although past societies could persuade people to committing atrocities and imprint into their minds that it is okay to do so, it mostly stemmed from fear, lack of knowledge and power play. Today we know better, well... Some of the time.
Most people in any time did horrible things thinking they were in the right so obviously most people shouldnt trust their moral judgment. It has been proven that some people use the part of the brain that deals with emotions instead of the part of the brain that deals with analytical reasoning when trying to decide whether something is appropriate or inappropriate. I dont think we needed science to prove this as its common sense because people have opinions without premises. But everybody thinks they are right and the rest of the world is wrong. Common sense just isnt that common. Otherwise people would know that they are probably wrong as their opinion is one of thousands if not millions where only one can be right. Humans suck and nothing we do could bring glory to god given all the bad we have done.