I don't agree with him, but I'll pray for his conversion. 
Question: if he is such a truth seeker and thinks the world is flat, then why hasn't he found Catholicism?
1. Discovering the truth about one thing doesn't mean you discover all truth. There are MANY men and women who have discovered the evil of abortion. But many don't have the Faith. Are we to dismiss the evil of abortion, since those "smart" "good" men haven't embraced the Faith as well?
2. The Faith is a gift from God, it is not something you can achieve by feats of mental prowess, study, etc. Prayer and grace are involved in any conversion.
We don't know what motivates Eric Dubay in his quest for the truth. Perhaps there is a lot of vanity mixed up in his motivations; maybe he likes being part of the edgy new age scene. Maybe the truth about flat earth is personally appealing or pleasing to him. I'm just throwing out ideas here; who knows the secrets of his heart (besides God). Every man's motivation is different -- EVEN FOR DOING GOOD and believing the truth. That is why only God can judge each one of us.
The ideal is to love the truth and will what is good (God's will) for no reason other than "God is good and deserves it". Unfortunately, men are seldom so pure in their intentions.