I don’t think you can relate Martyrdom with murdering someone for the Faith.
You can’t deduce that killing a heretic is okay, because God said “Thou shalt not kill.” He didn’t qualify that with “…except heretics, etc…” The proper fight against the heretic is fraternal correction as it is put forth in the Bible in the words of Christ:
Of course, if this is true, then self-defense is also not lawful since again, you said that he didn’t qualify his command.
If your brother sins against you, go and tell him his fault, between you and him alone. If he listens to you, you have gained your brother. But if he does not listen, take one or two others along with you, that every word may be confirmed by the evidence of two or three witnesses. If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector. Truly, I say to you, whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven. (Matt 18:15-18)
We are taught by our own Doctrines that justice is God’s alone.
**What authoritative document, explicitly or by force of tradition, states that heretics are not to be killed? In any case, this thread is about finding theological arguments against Aquinas’s opinion and therefore, to state that our own doctrines say not to kill heretics, is not to argue but to assert instead. Also, it is a question begging assertion. Also, it would follow that Aquinas is wrong only if all justice was God’s alone, but that is obviously not true -some is, and some is not and so the question ensues. **
In regards to Martyrs, they are killed by non-believers for their Faith. Their death is not something they choose, except that they would rather die than deny their faith. But you can’t then make a link between that and killing someone for a lack of Faith. All you are doing then is making a martyr for the heretics (and committing murder…and taking something that is not ours to take, but is God’s alone).
I think this is an argument from bad consequences or effects or emotion -either way it doesn’t follow from the fact that Aquinas’s argument would result in horrible events, that the argument is wrong.
ahs