I don't think there's anything wrong with forming an opinion based on incomplete knowledge. The problem lies in refusing to change your opinion when exposed to additional knowledge, which is probably tied to not wanting to flipflop after making an initial statement that turned out to be inaccurate. There's also the problem of not actively educating yourself if you need to make a decision with significant consequences.
I believe you must. I don't think anybody has complete knowledge of any non-trivial subject. Experts may have enough knowledge, experience and competence to form opinions, but I don't believe anyone has 100% coverage. History is full of examples of experts who were wrong too. We de facto work with incomplete knowledge and incomplete information. That raises the question then - how much is enough? I don't think there's anything wrong with forming an opinion based on incomplete knowledge.
I was reading an article that discussed the difference between an opinion and informed opinion. With an informed opinion you can argue your point and the debate doesn't fall apart in a second. The example they gave was actually anti-vaccine types debating with scientists. These people wanted their opinions to be heard and respected in the same way the scientists were but they weren't informed opinions at all. I guess we always form opinions on incomplete knowledge because really we can't know everything. However to form an opinion on no knowledge seems to be happening more or at least I'm noticing it more. I found this is a very common thing in the small town I grew up in where parents, instead of teaching their kids how to think, told them what to think. So now they have this opinion and you ask them why and they kind of just stare at you. I find this with many women too who just believe what their husbands said and don't actually question it. It's insane too me and others who have moved on from small towns. In my discussion with with one man he came into a conversation saying he didn't like what they were planning to do about First Nations issues this year so I asked what specifically he didn't like about the plan... He didn't know what the plan was. I can almost guarantee though, his father gave him some opinion about First Nations and he stuck with it because this is a person he respected. It's true about changing your opinion, and I think people are protecting their pride when they refuse to admit they made an error. Generally if I'm making an opinion on little knowledge I'll make that clear. Although some people see that as a sign of weakness I personally don't. I don't think having rigid opinions is a virtue because realistically there will always be something else we can learn. Having rigid opinions stops growth.
I think rigid opinions can be a virtue if the opinion is of high morality while everybody else's isn't. Refusing to cooperate in a crime when everyone around you wishes for it (for example, looting during a revolution because everybody already does) would have to be rigid so as to not let you fall under the "majority tsunami". Hell, starting a revolution because you believe the current regime to be oppresive and incapable of change on its own would require a rigid opinion to begin with. There's nothing to learn in both situations, but there's something to lose or miss out on. Would conforming be a virtue, then? I don't believe so: uncomfortable as it might be, you have to persevere for what you believe is right.I don't think having rigid opinions is a virtue because realistically there will always be something else we can learn. Having rigid opinions stops growth.