It seems that John is saying that there is no such thing as being either "heterosexual by nature" or "homosexual by nature," as a deeply rooted part of one's being. I'm not a scientist, but I can speak from personal knowledge and experience, and I think most people would heartily agree with what I am saying.

If you are only speaking about exploring "sexual experiences," based on "sexual desires at the moment," apart from any notion of a relationship with God or a conservative approach to life, this is probably true on a physical and sexual level for most people, if one is thinking about life in that way. But John is speaking of discussions about "sexual orientation and Christianity," and the born-again Christian is not looking for different sexual experiences, but desires a wholesome and committed life, and many non-believers are also interested in a committed life-partnership. The person who deeply understands themselves to be attracted only to the opposite sex, is not likely going to ever be interested in learning how to be in an "intimate love relationship" with the same sex, and the same is true for the person who is attracted only to the same sex, in regards to a relationship with a person of the opposite sex. John is saying that he believes this is "possible but not easy" for the straight man, for example, to learn and grow into desiring an intimate relationship with another man. (I don't believe many straight men would agree with him, but I don't know where you would find data to this effect.) "Gender" is a very important part of attraction and intimacy. It would not be a desirable thing to try to change in oneself, and I have no doubt that most people would agree.

Some people understand themselves to be bisexual, and can be attracted to either sex. In my understanding, there are two different kinds of "bisexual": One kind has only to do with engaging in "sexual experiences" with both men and women, and has nothing whatsoever to do with an intimate love relationship.

I will say, though, that the person who changes from understanding themselves as a gay person, and now feels that he or she is sexually attracted to the opposite sex, I believe was never innately homosexual in the first place, as many people feel deeply that they are, and as is evidenced for many gay people dating back to childhood. Some people are engaged in homosexuality, and it is related to other issues in their lives, and is not about being born with a homosexual orientation. I have no problem believing that this person can come out of their former feelings, and can move on the "spectrum" and become attracted to the opposite sex. This is possible especially with the help of God, as with any other addiction or issue in a person's life. It is wholeness and fulfillment in love that God desires for all people. The genuinely gay person finds fulfillment in a relationship with a member of the same sex, and just as for the straight person, this is not something that many people would want to try to change.