Necessary clarifications

Being gay can't be considered a sin, simply because it's not even clear what "being gay" means in the first place. Does it refer to a specific biological inclination? Does it mean a particular psychological experience? Is it meant to signify a concrete sociological action? All of the above? Nothing of the above, but something else? Unless this isn't clarified, saying that "being gay is a sin" is nothing but a rallying cry appealing to identity politcs. It's that simple.

Sociological action is undoubtedly a social construct, as it constitutes deliberate acts performed by individuals.

Even though biology as a science may be at least in part a social construct (as it concretely actualises within human society and is carried out by deliberate action of humans), biological inclination doesn't seem socially constructed but determined by natural processes.
(That is, unless you want to classify each and every human being in themself as being but a social construct - after all, humans come from the deliberate acts of other humans. However, this point of view wouldn't completely hold up to scrutiny since biology can't be fully reduced to sociology.)

Eventually, psychological experience seems to occupy a middle ground: firstly, its basic limits are determined by the biological disposition (e.g. humans can't experience what it's like to be a bat); secondly, the particular psychological experience is at least partly shaped by the social environment of the individual, i.e. by the will of other people (e.g. education through family and school, or cultural background); thirdly, psychological experience is also shaped from within, i.e. by the will of the individual itself (e.g. self-reflection with regards to options and circumstances).

So, biological, psychological and sociological traits describe the natural, habitual and voluntary elements of what it means to be a human being.

• Natural traits can't be sinful in themselves, full stop (albeit they may be classified as being disordered according to and only in relation to certain manners of ordering them).
• Psychological traits can in principle be sinful insofar as they come forth from the will of the individual, but they can't be completely sinful considering the following: with regard to their origin in natural traits, they simply can't be; and with regard to their origin in social shaping, their sinfulness lies with the other people being responsible for said shaping; it is only as regards the individual self-reflection of options and circumstances that they might be sinful.
• Sociological traits, eventually, can be sinful in themselves and in the full sense since they stem from particular acts of the will.

All of these traits overlap, if you want to put it that way, in the individual human person. However, persons are not sinful per se. So, the abovementioned clarifications are still necessary: What does "being gay" mean?