Gutsy to ask such an unpopular question. Still, your question is painful. The idea that only those in your community ought to receive aid when it is needed is deeply flawed.
“For if you love those who love you, what recompense will you have? Do not the tax collectors do the same?” Matthew 5:46
But then, that is not really what you are after. You want to know if corporeal assistance to a person who is in need of spiritual confirms or aids his disbelief. The answer is no. You can go to scripture, as some have, for answers, or to the example of many, many saints. But since you have brought up St. Thomas as an authority, lets go there:
On almsgiving, article nine:
“
Objection 1. It would seem that one ought not to give alms to those rather who are more closely united to us. For it is written (Sirach 12:4-6): “Give to the merciful and uphold not the sinner . . . Do good to the humble and give not to the ungodly.” Now it happens sometimes that those who are closely united to us are sinful and ungodly. Therefore we ought not to give alms to them in preference to others.
…
Reply to Objection 1. We ought not to help a sinner as such, that is by encouraging him to sin, but as man, that is by supporting his nature.”
He is speaking of whether we should care first for strangers or to those more closely united to us, but he speaks to your question as well. We cannot encourage sin. We do not aid the sinner as a sinner, but as a man. That is, in providing for his corporeal needs we do not confirm his sin.
Elsewhere in the same section, he discusses the difference between spiritual and corporeal alms. That is worth a read for this discussion.
newadvent.org/summa/3032.htm#article9
Also, I am not sure where you get the idea that killing sinners, self defense, community justice and war justifications notwithstanding, is something that St. Thomas would or did defend.
He did indeed, in discussion of murder, allow that killing a sinner is not necessarily evil. But he went on quite clearly to say that it is not allowed or defensible for a private individual.
“On the contrary, Augustine says (De Civ. Dei i) [Can. Quicumque percutit, caus. xxiii, qu. 8: “A man who, without exercising public authority, kills an evil-doer, shall be judged guilty of murder, and all the more, since he has dared to usurp a power which God has not given him.””
http://www.newadvent.org/summa/3064.htm#article2