Does Whether X is a Choice Matter to How It Should Be Legally Treated/Addressed?

Hoisted from the draft queue from 3/5/14:

Why does it matter whether or not a controversial potential subject of legislation is a choice or not?  For example, why does it matter whether homosexuality is a choice or not?

Plenty of people who support gay rights make the argument that they should not overly rely on their involuntary nature—that’s an empirical fact, and may change as new information comes to light or even if technology emerges that makes it changeable, rendering the choice to use it or not equivalent to the choice of whether or not to be gay.  What matters is whether or not it’s chosen, on this view, but whether or not it affects/harms others who haven’t chosen to be so affected/harmed.

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But, on the alternate view, whether or not an action is a choice matters because criminal sanctions on inactivity are meant to reduce that activities rate of incidence.  

So if a certain behavior is not a choice, then those who embody/manifest/engage in it will persist in doing so regardless of the penalties they thereby suffer.  In such cases, when the demand for the activity in question is quite inelastic (so to speak), erecting and prosecuting a system of criminal punishment against the activity's participants is pointless and unlikely to result in a change in behavior, and therefore does not justify its cost—either financial, in terms of the resources taken from others devoted to this purpose, or moral, in terms of how the targeted individuals are treated.

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Kant's 'ought implies can' seems relevant here: only if something is a choice do moral issues exist there.