True, but I've never liked FTS :D
Was thinking tag->object + existing fts, reason being is that it seems more likely that people would use short tags rather than search for every occurrence of a short word like "the" or "and".
Still leaves us with the "sex" problem, but it might be a reasonable workaround.
Of course, it might be better to replace FTS with a dedicated tool which maintains its own (ACL aware) lookup table. Mysql presents the Known problem as well (where "known" is, rather embarrassingly, a kill word).