To the modern man, it seems wrong to believe that you can actually "know the truth", and therefore be in a position to "answer" the false religious claims of others. While an open mind is indeed a good quality, that open-minded nature ought to eventually settle on something it has tested enough and studied enough to "know the truth," and if one remains open-minded to the point that one cannot admit of knowing "the truth" on anything, then one cannot actually settle on believing in Jesus with any degree of certainty. After all, a large portion of the world does not agree that Jesus is the Christ, the Son of the Living God, and you would have to remain open-minded on that as well.
I am willing to re-think and re-test anything I believe, but what I believe is based on much testing to the point of decision. If I have decided that I have tested something to the point that now I believe something, then I will speak and write what I believe is true. I will not speak or write unless it is with confidence that it is true to what God's word has revealed is true. That is not to say that I am not willing to change my mind if someone comes along with better evidence than I had considered before, or evidence I was not aware of that would have tipped the scales of judgment in another direction, but, I do believe that it is right to believe with conviction that some things are true and some things are false.
The Lord Jesus is the One who said that continuing in His word would result in "knowing the truth, and the truth setting us free"(John 8:31f). Take a concordance and look at the number of times that the New Testament writers speak in regard to knowing "the truth". They did not tell disciples of Christ to just remain in limbo, always open-minded because they could not be certain of "the truth".
There was no shame in claiming to know the truth, and there was no arrogance in making such a claim or drawing out such a conviction. Confronting error with truth is what disciples of Jesus did in synagogues and market-places and in school-houses and riverbanks. They knew the truth and they believed that others were in error and needed to know the truth to be saved.
While it may be true that we do not individually know all the truth on every topic imaginable, it cannot be the case we should never claim to know the truth on anything. The free-thinker should think and study and analyze until he knows some truth on at least some things. If he thinks that it is wrong to claim to know the truth on anything, then he simply does not know Jesus or God.
John Clark observed: "When we narrow our minds by the acceptance of the truth and the rejection of error, we are not restricting and paralyzing ourselves. We are really freeing ourselves. Who is really free to go from Louisville, Kentucky to Nashville, Tenn.? The one who strikes out on any and all of the 360 degrees of the compass or the one who accepts the fact that there is a certain direction one must go to get there? The "narrow mind" on this matter is really the one that is freer to get to Nashville easily. A mind narrowed from "every way" is then free to go "the right way" (FC Lectures,1974. P.268).
When the apostles and elders engaged in "much dispute" with the ones who were teaching that Gentiles should be circumcised and keep the Law of Moses (Acts 15), the apostles and elders did not remain "open-minded" and encourage everyone to just keep an everlasting open mind because no one could ever be certain of truth. No, they debated the evidence, looking at all the evidence and then coming to a conclusion of truth, determined it should be shared with others. Every belief was not equal, and every belief is not true. At some point, the testing of a viewpoint should result in a conviction. There is no virtue is remaining in a constant state of indecisiveness all in the name of keeping an open mind. If we cannot look at the evidence, test it and analyze it and then conclude that "this is the truth", then we cannot know the truth and be set free as Jesus claimed.
There are things that are clear, and things that should be getting clearer. The Bible does not treat all beliefs as equal. Neither should we! You cannot read of Jesus and His disciples just keeping an open mind to others and other beliefs. They knew the truth and when they knew it, they stood for it, and confronted error with that rock-solid-truth.