"The presumption seems to be that straightness is normal and therefore does not need explanation; whereas queerdom is a deviation from the norm and this requires investigation and answers."I'm not sure he's right about that; the search for the 'gay gene' or whatever to prove that people are 'born gay' is more frequently cited by people sympathetic to the cause of gay rights and is used to demonstrate that this particular orientation is as natural as being born left-handed or ginger-haired or whatever.
While I'm sure Tatchell is right to reject deterministic explanations, it is in any event irrelevant if someone is born gay or not. In this sense, he's right that the attempts to uncover the biological determining factors behind homosexuality concedes far too much to those who believe it is something that requires justification. Even if it could be demonstrated that, for example, that psychopathic mass-murders were 'born that way', no sensible person would conclude therefore that mass-murder is ok. But obviously homosexuality is not like that and those of us that take the 'harm principle' stance believe it is for those who say homosexuality is wrong to make arguments and provide evidence for their view. In this context, whether it is a 'lifestyle-choice', or determined behaviour or a mixture of both is entirely irrelevant, surely?