Contemplation of repulsiveness is not for the purpose of developing aversion, which would just be replacing one defilement (lust) with another (aversion). Its about the removal of lust, and the cultivation of disenchantment, insight into impermanence, and arousing of (samvega). With insight gained, one can see that beauty and repulsiveness are both just habitual perceptions — without it, one will be swept away by the perception of beauty and lust will overwhelm the mind.
It was taught to monks who were observing full-time chastity, not for lay persons observing five precepts. It can also be practised by lay people, but is not often taught these days, except perhaps in forest monasteries.
One should always choose a meditation suited to one's temperament — that is why there are many different methods included in the Satipatthāna Sutta. Try mindfulness of breathing or analysis of the four elements if contemplation of repulsiveness doesn't work for you. For cultivating tranquillity, one can use recollection of the Buddha's qualities, or the Brahmaviharas — loving-kindness, compassion, sympathetic-joy, and equanimity.
• • • • (Upasampadā: 24th June, 1979)