In my honest opinion, I feel like Harambe would not have, intentionally, done any major/fatal harm to the boy. I mean, from everything I've watched about this, he didn't seem like he was going to hurt him, he seemed like, for the most part, he was just kinda being there with him and yes, he did drag him which isn't exactly good, but, let's be real, it was just to get him from one spot to the next, not to hurt him.
Now, I can understand the fear the kids parents, or parent, must have felt when he fell in there, and when they saw Harambe dragging him around in the water. Obviously that's a scary situation. I can't even begin to tell you how much I'd be panicking if that were my kid, and it's so great that he came out of that barely hurt (and probably with a newly developed Gorilla phobia) but I really think they both could have come out of this situation alive. It's true that a tranquilizer would have probably freaked out Harambe and made the situation possibly dangerous (and i mean, he and the kid were in a moat, Harambe could have drowned if he were passed out in the water and in the event of him passing out, there's the possibility of him falling over on the kid and hurting the kid, or trapping the kid and then the kid drowns also, or at least gets seriously injured from the weight and impact), but again, he was confused/agitated because people were yelling and freaking out and he had no idea what was going on or what to do with this small human who had fallen into his living space.
Watch most if not all of the videos on YouTube of Gorilla's that find themselves in a situation where a small individual has fallen into their enclosure and you'll see they're not violent. Most will actually take care of the kid or protect the kid the same way they'd protect their offspring, I'm sure. Really the only violence in this was him dragging the kid through the water and as damaging as that was, it was only to get him from one spot to the next. I can assure you, if he wanted to hurt or kill that child, he would have. He had just enough time to do so.
What's done is done, but it's unfortunate that Harambe had to die, especially under these circumstances.
"When gorilla or other apes have things they shouldn't have, keepers will negotiate with them, bring food, their favorite treats, pineapple or some kind of fruit that they don't know and negotiate with them,"
"I don't know if that was tried or people thought there was too much danger but it does seem very unfortunate that a lethal shot was required."