We are fallible: we can and do make mistakes, often. Therefore we have a great need for mistake (error) correction. Mistakes cause bad things like suffering. The way to correct mistakes is to find or notice bad things, criticize them, and come up with better ideas which will solve the problem. Criticism consists of explanations of mistakes: what the mistake is, and why it's bad.
Creating knowledge (learning) consists of imaginatively coming up with ideas and then using criticism to correct mistakes in them and thus improve them. No method of creating ideas reliably creates good ideas directly. Ideas have to be improved. This process is called evolution and the creation of knowledge in genes is another instance of it.
In science, we refer to evidence in our criticisms. When an empirical claim does not match the physical facts, that's a flaw in it. However, even in science most ideas are never empirically tested, but instead are rejected due to philosophical criticism first. Ideas need to be good explanations. They should be non-arbitrary, solve some problem or answer some question, be clear, understandable and unambiguous, be self-consistent, and not contradict any existing ideas which we have no criticism of.
A rational lifestyle (way of life including policies, institutions, traditions, ways of thinking, philosophical attitudes, background knowledge, etc) is one that does a good job of correcting mistakes rather than repeating mistakes. It's important because mistakes are common and uncorrected mistakes hurt people. It's also important because it's a knowledge creating lifestyle and knowledge lets us solve our problems and make progress.
An important way to judge a lifestyle is by how it treats disagreements or conflicts. When there's no disagreement or conflict, life is straightforward; everyone agrees about what to do, and doesn't see any problem with it, so just do that. When there is a conflict or disagreement, a rational lifestyle will not use force but will instead focus on critical discussion and persuasion with an aim towards conflict resolution.
Getting your way by force is bad because winning a fight does not magically make your ideas good. Force does nothing to improve our ideas, nor to evaluate which are good. Force also hurts people, and using force risks losing the fight and being hurt. When we use force, we do not correct our mistakes; choosing for conflicts to be determined by force is an irrational lifestyle. The only reason to use force is if the other guy has decided the disagreement will be settled by force, thus precluding a rational outcome or any learning, and so you're just using force to defend yourself.
In a disagreement, it's crucial for me to remember that I may be mistaken. My goal should not be to get my way, but rather to consider that the other guy's ideas might have some value, and this is an opportunity for both of us to learn something. Clashes of ideas can help us discover flaws and improve.
The first rule of conflict resolution is that the harder time you're having coming to an agreement, the less ambitious you should be. If you can't cooperate to mutual benefit, don't cooperate. Go your separate ways. If one person wants to end the discussion, and he's under no clear, specific and binding obligation to carry on (examples: people are obligated by contracts they agree to, and parents are obligated to feed their children), then the discussion must end. The reason the discussion must end is that there's no way to continue it without using force to prevent the person from leaving. Of course if you can tell him a good reason to continue then go ahead, but if he doesn't want to listen to any more of your ideas there's nothing you can rationally do about that. He may be making a big mistake; but on the other hand you might be; to think that using force to get the outcome you think best would improve matters is to assume you are right, but in a disagreement you might be mistaken. Plus fighting is destructive and you might lose.
Conflict resolution does not just apply to disagreements between two people. It its purest form, it applies to disagreements between ideas, which may both be within the same mind. In this case, going separate ways is not an option, but there is a solution. Conflicts of ideas are only dangerous when there is a decision to be made, otherwise we can just peacefully ponder them until one day we come up with an answer. If we can't resolve a conflict directly in time to make the decision, we can consider the question, "Given this conflict is undecided, how should I make the decision?" This method can be repeated if further conflicts come up. In this way, decision making can continue while an unlimited number of conflicts between ideas remain. All we need is one idea about what to do which isn't in any conflict and which we have no criticism of.
Learning in general is about creating one single idea. Whenever we have multiple ideas, we don't know what to think. But we use criticism to eliminate mistaken ideas. When we get to exactly one idea, then we can tentatively accept it. What if we have two conflicting ideas and can't think of any criticism of either? Don't worry about it too much, maybe you'll come up with a criticism later, or someone else will. And what if we have to make a decision that depends on this conflict? Then use the method above: consider the conflict undecided and come up with a decision compatible with that. And what if we have zero ideas that survive criticism? Then come up with one idea about what to do which is compatible with not knowing the answer.
Liberalism is this rational style of decision making and conflict resolution applied to political questions. For example, liberalism highly values freedom, and freedom means that you can live your life without anyone using force against you. The Government uses force (and, more often, threat of force) routinely, and therefore the Government should be improved to use less force and, ultimately, not to use any non-defensive force. The free market is freedom/liberalism applied to economics. It recognizes that force never helps anything, so it insists that all interactions be voluntary.
Morality is rational epistemology applied to decision making. In this way, one will never hurt an innocent, will resolve all his conflicts amicably (unless the other person irrationally prevents that), will solve as many of his problems as he can, and will have the best life he knows how to. And one can do this while always learning so that his problem solving capabilities, and the best life he understands, continuously improve.
In each of these fields, there is an objective truth. That is necessary to agreement and consent and voluntary cooperation and so on being attainable. If every arbitrary idea was as good as every other, people would have no reason to ever change their minds or care what anyone else thought.