#if that ain't the copyrighted Uchiha coping strategy then what is

[whether-to-screech]

If we are being technical about it, Obito definitely regretted a lot of political and economical miscalculations or coincidences he did not or could not predict 😅

Aside from every major or personally hurtful fail...

Frankly, I do not think Minato's death and everything around it would make it on the list of regrets - partially because, well, Minato did fail Kakashi, the only kid he was still responsible for, big time, and quite a lot of Obito's reasoning was about "well, I suffer, Kakashi suffers, let's drop this gig"; also, not being there for Rin (which was like a year before N's birth?). Main reason, though, imo is that Obito was in a very bad place then, conviction-wise. You can't convince me that he completely switched his world view in a year, it's just not done, his brain would not have dropped the associations and thought patterns it got used to so fast. So, he definitely felt at least somewhat guilty, after. And what do you do if you are guilty over something you did for "the greater good"? You rationalise why it was okay or a right/only decision. (See Dumbledore sending Harry to Dursley). The seal would have broken anyway, Kushina would definitely have died from it, Minato would likely still sacrifice himself one way or another, no matter if Obito made some rude small talk and controlled the beast or not. And the concept would have stuck to the point where it is a fact that Obito didn't question anymore.

Kiri is unlikely for the same reason, "Yagura would've still done it, I just chose the specific actions"/ "those kids would've died anyway, only causing even more bloodshed prior to that", etc. Plus, of course, personal vendetta.

Massacre? Dunno, really depends on what his relationship with the clan really was, if he had any positive interaction with anyone, if his grandma was still alive why is it never touched on??? If they were just a bunch of rich folk who refused to associate with him I guess it wouldn't be that hard. Besides, again, Danzo assigned Itachi to do it anyway. Ostracizing Uchiha? As far as I recall Obito did not do anything about it aside from controlling Kurama, so it was actually the justification, the proof of how rotten the world was, the fellow villagers hating so easily, Uchiha turning to violence as solution, Hokage allowing it because friendship goals. It's also easy to dehumanise people if you do not let them talk to you as you kill them after being absent for almost ten years. Just another shinobi to fall, and what do a last name and clan insignia even mean in the large picture?

Kisame is likely to be a regret. I'd feel guilty over being the reason for his death, especially since the secrets he was keeping were a moot point. Deidara, maybe, if we think that Obito liked the kid?

Aside from those, Onto does not strike me as a person who regrets the actions, unless they concerned specific people he cherished - and there were super few of those. Otherwise it's "Welp, I'm a bad apple, shame about it" and just embracing it all. I'd add Kakashi, but he was more of a collateral, except for when "Tobi" reveal happened, and the Chidori scene, but that does not really seem to count since it was part of the ongoing situation at that moment.

TL;DR

Not many regrets whatsoever. Maybe missing the shark and regretting making a fool of himself when negotiating for trade routes through Kiri when he was like 17. Otherwise, he either felt like he made no difference because of the shinobi society's inherent violence and flaws, or had convinced himself he was right and justified even if originally he might've not thought so.

In one of my last posts, I mentioned that there are probably some actions that Obito has little or no regrets about doing. What do you think that would be?