David's sling-shot: yes, but David was in a military situation - the Israelites were under armed attack by the Philistines.
That doesn't give you an excuse for knocking down someone for their opinions. Next stop, political assassination.
We need to know that the man actually WAS a repentant Catholic reconciled to tradition. WAS he attended by an SSPX priest?
Supposing that the man was repentant, but was attended on his deathbed by an NO man - would the SSPX provide a ceremony?
If 'yes' for him in that case, then why not for any other NO supporters who happen to die? Surely it can't be his secular political beliefs that ensure favourable treatment?
What if he DIDN'T kill a single person but still stuck to his nαzι beliefs? nαzιsm and Catholicism are mutually irreconcilable.