These are the flaws of why D-Fens is ultimately a bad guy and his behavior is unjustified.
For those who still think that D-Fens has any justification for his behavior, here is my list of why he does not.
1. He is a hypocrite who demands respect from other people, yet he doesn't care to show much respect for them, criticizing them for doing things that he easily does (calling out the shopkeeper for being a thief and then stealing his bat for basically no reason, calling out his ethnicity when he later criticizes the Neo-Nazi for doing that).
2. He becomes disproportionately angry over petty incidents (no change for the phone and not being able to have breakfast when it's lunch).
3. He has no problem using force to get what he wants, showing that he is aggressive and entitled.
4. He never explains to his ex-wife that he can't pay for child support because he lost his job, and also lies to his mother he is still working.
5. He repeatedly showed up in the middle of the night without permission and knocking on the door, disturbing his wife and possibly freaking out his child. He then continues to try and establish contact with them after the restraining order has been served.
6. He blames his mother for the divorce and losing custody of his child, even though there is nothing in the film that indicates that she had a big hand in it. He is also very cold to her and shows a lack of consideration for her. It is likely that he hates living under her roof, and can't even be grateful that she gave him a place to stay.
7. He casually steals weapons and items from multiple scenes. Morally, you have no right to take something that you know belongs to someone else, even if they aren't present. Nothing indicates this was caused by his mental breakdown.
8. He shoots the guy in the leg who tried to kill him just to rub it in his face, despite knowing he can ignore him as the dude will likely be arrested.
9. Prior to him passing "the point of no return", he blatantly has no regard for the restraining order against him, despite knowing it could get him in trouble, showing he doesn't think of the consequences of his immoral actions.
10. Has no empathy for the guy who is having a heart attack, and taunting him after realizing he can't help him.
11. He embraces and kisses his ex-wife despite her lack of consent and tells her that they are still married. This show he is obsessive and delusional.
12. He pulls out a gun in front of his daughter, despite knowing that she's in his presence. No parent would do that if they were sincerely devoted to their child. It's possible he may have been planning on murdering his wife, even if not his child.
I think that's the most I can think of right now for the moment. D-Fens may not be an evil person, but he certainly was willing to do evil things for his own personal gain.