With all due respect, is it necessary or encouraged to consult with a rabbi for everything? Can't a person have some independence and make decisions for himself? And even if he ends up making the wrong decisions, he'd learn from his mistakes and at least develop the ability to make the right decisions in the future, rather than always relying on a rabbi.
I appreciate the points you make. The answer is that, as in all spheres of life, it is not always necessary to seek guidance and advice, but it is usually advisable.
It is also relevant to distinguish between questions having to do directly with Torah teachings of right or wrong, permitted or forbidden, kosher or not kosher etc., as opposed to questions of advice, where the wisdom of the Torah may be pertinent, but not imperative.
In the first category, if a person knows the Torah teaching or law himself, of course there's no need to consult. But if the topic is not necessarily well-known, or accessible, or if the person has some doubt, or otherwise some bias which may prevent him from making the right decision, he should certainly consult an expert.
In these cases it's not relevant to suggest learning from mistakes, because in the meantime he's likely to transgress the Torah when he could have consulted a rabbi and avoided doing wrong.
In the second category, that of advice, while one could assert his right to make wrong decisions, wouldn't it be better to exercise his privilege to make right ones? Why reinvent the wheel through a series of wrong tries? Assuming the rabbi is intelligent, older, experienced, and possesses the insights of Torah, why not seek his advice on any matter?
Think about it logically: If, after working through an issue thoroughly and coming to your own conclusion, you consult a rabbi and he agrees, you've done well. And if he presents considerations you didn't think about, reaching a different conclusion with which you agree, you're even better off since you've been spared the mistake. And if after discussing it you remain of different opinions, you're entitled to make your own decision.
But making mistakes is not the only way to learn. In fact it's probably the worst way to learn. Seeking advice before you make decisions is actually the best way to learn how to make the right decisions on your own in the future. In the meantime, discussing decisions with people like rabbis will give you the insight and experience needed to simultaneously penetrate an issue while considering all its facets in order to make decisions that are consistent with the wisdom of the Torah.
And, believe me, the people you seem to be reluctant to consult certainly spent decades consulting their own rabbis before being in a position to advise others. And thus back to Moshe at Sinai. But if you connect yourself to this system properly with humility, eventually, not only may you not always need the help of a rabbi, you may become a rabbi who helps others!