Saying that people can choose to become queer does not necessarily imply that people can also choose to become hetero. It might be that in a society where girls and boys are raised to have so little in common, exclusive homosexuality is really the healthiest option for any of us, in which case anyone who's already discovered the joys of same-sex attraction could hardly be expected to ever develop much interest in dealing with all the inequalities and communication difficulties of opposite-sex attraction. Or it might be that bisexuality is the natural state of all people, in which case discovering our ability to feel same-sex (or opposite-sex) attraction would be much easier than trying to repress that attraction after we've discovered it.
Some queer by choice people do believe it's possible to choose to turn hetero—which most definitely does not mean we'd ever care to do it! Others of us believe it's not possible. Some of us simply have no opinion on (or interest in) the subject.
But even if we could block out our same-sex attraction and develop exclusively hetero attraction again, what would be the point? In most people's minds, heterosexuality is something like virginity: once you've experienced being a nonheterosexual, they're not going to let you get away with reclaiming your former hetero privileges even if you do want to reclaim them. Hetness and queerness are not really defined symmetrically as "attraction to the other sex" and "attraction to the same sex." Instead, you might say that hetness is defined as the state of "never having been attracted to the same sex" and queerness is defined as the state of "ever having been attracted to the same sex." So at least in that sense, no queer can go back to being a hetero any more than we can go back to being a virgin.