The Church does not use the words "hetero/bi/homo sexual."  It refers to same-sex attraction and distinguishes it from same-sex acts.  The continuum of which you speak is not one of immutable, inborn orientation; it is a continuum of learnable attraction with most people experiencing an environmentally-influenced predisposed attraction predominately to one sex or another or both, but completely extendable to both or retractable to neither based on any number of external factors.

Modern psychology is junk science, used as a political tool to promote what is easiest for people to deal with; that is, rather than point people with same-sex attraction to normal sexual relationships, allow them - and convince society to sympathize - to stick with their predisposed sexual attraction.  And then come up with various theories like "sexual freedom" (wait, that didn't work), "sexual preference" (wait, that didn't work), "born that way" (ding-ding, we have a winner) to make it seem scientific.