If you haven't read Daredevil: Father, stop reading this blog it is essential you have read it or else it doesn't make sense and will spoil a very good Daredevil story. Consider yourself warned, There will be no spoiler alert/spoiler marks.
Read the story? If yes let us roll, if not your problem.
Now I first breakdown the scenario and afterwards give the reasons why it was wrong by Matt to save the old man.
In Daredevil Father the lunatic serial killer Socket goes around and killing people Matt has had as lawyer because she had an obsession with Matt Murdock. Now her father was the old kind blind man Matt saved. Kind as in the Silver Age now in the modern day he is a father who molested her own daughter. This is given as some of the reason or at least Socket does show when she whispers to Matt. Now how has this anything to do with Matt and why does that make saving the father a morally wrong choice you might ask.
Well if we look at utilitarianism (a moral theory primarily found among English philosophers). This theory was first coin by Jeremy Bentham. The idea is that you should act so that greatest aggregate happiness among all sentient beings, within reason. Therefore it was wrong since it would had stopped Maggie (Socket) from getting molested or it would never had happened. There is not being given a clear time for when it started nor stopped. I would say Maggie is around the same age as Matt, but that is a guess. Matt would also not have been blinded. Now Maggie and other people could have been depressed if her father was died that day. However that is though to call who many and how sad. Directly we only have Matt sadness about being blind and Socket sadness for being molested. However you could take it a step further. Let us say that Maggie never would have become Socket if the father was died that day. Wouldn't it then have been better if he had died? Well for Maggie and Sockets victims without a doubt. But this day also changed Matt Murdock it is because of this that he could become Daredevil. Daredevil has all things put together in a utilitarian viewpoint done more good than harm (or at least I believe so, if not there would be no reason for being a vigilante) even though Matt's life as Daredevil also has given a great deal of pain his friends, families and love ones. So all in all it is rather tough to call if it was right or wrong to save the man's live. However I think that Matt's is regretting he saved the man's live. I think Matt believes it wasn't worth for him and it have been better of just let him die. no, I'm not saying you shouldn't rescue a man (or woman for that matter) if he/she is about to get hit by a truck. The point was more to take a philosophic view of the most important day in both Matt's live.