Unfortunately, since the entire "reasoning" of the generally-lazy public, with short attention spans and dumbed down (on purpose) by the modern educational system, the most effective way to combat these types of "arguments" is to simply call out the (loosely-stated) principle of "two wrongs don't make a right" (a variation on end does not justify the means) and to lay out other scenarios.
Let's say I have a child or spouse or parent who's run over by a drunk driver and now becomes a paraplegic, where a caregiver must now feed the person and change their diaper, etc., providing constant around-the-clock care.  So, because of the evil that this driver did, am I permitted to kill this person due to the burden that I have now incurred as a result of the evil action?  Am I permitted to effectively punish the victim again by taking their life?  [Let's say the person wants to live, to take the "euthanasia" angle off the table for this scenario].
So, if the unborn child is a life and has an inalienable God-given right to life, we cannot punish children by murdering them even if they came about due to some evil act.  While the burden to the victim mother is regrettable, it doesn't justify punishing the child for it, i.e. two wrongs don't make a right.  We should enact legislation where in such cases, the state would provide a victim compensation fund to help raise the child and perhaps even facilitate an adoption (in a Catholic state to good Catholic parents).
Of course, even the human "right to life" is a little bit off.  What's key here is really God's sovereign rights over life.  So, if we insist that the right to life is primarily in the individual, then things like "euthanasia" are harder to fight off, where it's "their life" and so they can do with it what they want ... and it also, conversely, makes it difficult to justify capital punishment.  Again, the faulty framework that the human being is the primary possessor of the right to life, rather than this being a question of GOD's RIGHT OVER LIFE ... compromises the Catholic approach to these other issues.
So, until the reign of Christ the King over a Catholic society has been re-established, there can be no true victory over these matters, since we're operating in a non-Catholic relativistic framework, and swimming upstream, as it were against it ... although, as we're seeing, many even Trad Catholics are just going with the flow and jettisoning Catholic principles instead of swimming against this tide by adhering to them.