Its hard to condone with a liberal whose views on freedom and equality contradict morality, esp. Chasity. If I make a point that the body is the soil for the tree of the mind and to keep itself pure, renunciation from lust and greed is necessary, they make a contention that no one size fits all and not everyone is a ardent purifier of self.
The problem with a liberal is he is a zealous enunciator of freedom of thought and action, thus he will not take side of any one of disparaging factions, so its harder to convince him the universal benefit of Islamic philosophy and morality.
One point that aggravates the situation and one that most of my Islamic brothers like to make is zaid leads to unwanted pregnancies and plethora of bastards who corrupt themselves belonging nowhere and the society, though true for medieval times, with the easy availability of contraceptives, this argument does not hold true anymore. Besides the "bastard problem" is not something that cannot be fixed by therapy, liberals exhort. Thus the assertion on chastity and its implications if not followed is weak.
With all this in mind, how can I make my argument strongly rooted in Islamic philosophy in a rational manner concurring to a liberal?