The logic of an argument, however sound, could do little to sway a moral relativist. People use relativism to justify there own sins or to justify the negligence of not interacting with others to promote fraternal correction. Many relativists shift the focus on feelings and community attitudes rather than the reason of the mind.
The best approach is the trust consuming dialogues to the topic of worldviews. This takes place when you enter their world. The humble associate will allow the friction to get to the core of what needs to be said. This mode of the layperson, a “private individual” (STh Sup., q. 31, a. 1, Rep. 1) represents the best in this approach in the cause of effectiveness given they participate. While the “public officials” have better access to the duties of penance which all are called to perform - from which the perfection of life is pursued, the example is illuminating and the preaching has done to affirm the dialogue of the laity. Not that priest forfeit dialogue. The lay people who communicate with the sacraments are internally bound to speak to them. But the priest has a better position to indicate the divine at work in the world, and thus they have to be busy at the divine work. And that position inspires others to pursue their private work in a divine way. This can be equivocal so take this with other viewpoints.
I got off topic. Anyway, what makes an act hypocritical, according to the Angelic Doctor, is the performance of deliberate lying by the act itself. To act against abortion would be a lie if the person was not really against it, and intended to deceive. To act against eating meat would be a lie if the person was not intending on abstaining, and intended to deceive. The baby is not meat so they are not mutually exclusive.