I don't understand what is unclear. If this is a textual derivation, one can refute it; and if it is a logical argument, there can be a better counter-argument.

A better argument is not enough. In order to disagree with the Sanhedrin, certainty is required. I don't see how you can reach a state of certainty about this.

I have the same level of certainty that I would need for the requirement of certainty in order to disagree with the Sanhedrin.

If possible, could you also give the reasoning for your statements—both for the principle that there is no obligation, and for the requirement of certainty. Thanks.

You yourself wrote why one should not listen to the voice of the Sages, since their authority is no greater than that of the Sanhedrin. The assumption is that if the Sanhedrin errs, there is no obligation to listen to it (this is the topic of one who errs regarding the commandment to listen to the words of the Sages, at the beginning of Horayot).
The requirement of certainty comes from simple reasoning. If everyone who disagrees with the Sanhedrin does not need to listen to it, then its authority is empty of content. Exactly as a soldier's right and duty not to obey an order exists only in a case of a "manifestly illegal order"—that is, when it is completely clear that the order is illegal, and not every time it merely seems to him that it is illegal.

So why is anyone who is learned and reasons independently considered to be relying on his own judgment? Has every person immersed in the world of Torah reached a certain conclusion against the Sanhedrin? If, in your view, such a person is required to obey the Sanhedrin as an authority [and not merely as a clarification of Jewish law], then the sin does not rest on his shoulders.

One who is learned and discerning, and has reached a clear conclusion, is relying on his own judgment. What is unclear about that?
And see there the law of one who rebels against the ruling. And all this applies to one who is learned and discerning, which each person must decide for himself whether he falls into that category. And one can further discuss whether ordination and authorization to judge are also required here, which do not exist nowadays.

You are concerned about one who disagrees with the Sanhedrin, while the Torah is concerned only with one who rules according to his own opinion against the Sanhedrin. And perhaps you too are concerned with that, and therefore do not issue rulings against the Sages?