Calling it a biological defect or flaw is a hidden moral judgment, because it really isn't a biological flaw and so your reason for arguing that it is could only stem from trying to rationalize your own personal moral objections to homosexual behavior.
Hidden moral judgement, seriously?

Anyway, you've ignored the sugar point, I suppose I worded it poorly but what my point was is this.
Humans developed reward/motivation systems to encourage beneficial activities. Things such as eating give us pleasure, if it didn't we wouldn't have searched for food, we would have just waited for some to come along. When this motivation for food evolved, the group of animals (this was probably a very very early development) evolved to be rewarded by food, they dominated. Thus we are all decended from that first group of fish who had the advantage of being motivated to eat. This is why sex is so enjoyable.

While the group of fish that didn't have a motivation for eating probably lead an normal life with their mediocre food, they clearly had a disadvantage which is why the other group dominated.