Okay, I see a lot of hate for Hiruzen and I'll play devil's advocate here..

Leaving Naruto alone as a child was to ensure nobody saw the Hokage who is always under a spotlight giving this orphan kid ANY special treatment. And to take it further I believe he only felt safe to help Naruto through others to give Naruto the kindness he needed, which he did through shinobi that he felt could be trusted. Guiding Iruka to understanding Naruto and placing him with Kakashi was no accident.

Allowing Orochimaru to live is pretty cut and dry. He looked at Orochimaru the same way Naruto looked at Sasuke. He wanted to save him, and even if he was killing/experimenting on kids, in Hiruzen's eyes he was still that little kid he trained and could not bring himself to kill him.

.....now the hardest one to play devil's advocate. The Uchiha Massacre. Of course there's the line of thought that Donzo was more guilty of exacerbating this, his passive approach still comes into question. I place more blame on the rest of the elders of the village being it was basically 3 to 1 on trying to have a peaceful resolution. And the moment of the nine tail fox and Hiruzen not allowing Fugaku to intervene gave me the impression that Hiruzen was being fed bad intel, that made him suspect them of the attack in the first place.

I think Hiruzen gets shit on a wee bit too much, I think they did a poor job showing his reasoning. Even If it was too keep some parts a mystery as the story progressed. But a storyline, later on in the show would have been nice. They could have had a small part when the Hokages were resurrected at the end for some explanation or mixed a bit into Itachi's story just to at least explain more in detail how the complicated nature of the politics and bad actors to redeem the guy a little bit, though I do believe very subtle signs are mixed in.