Thinking about the hate plague again in relation to KYHAW and Bee not even physically attacking Optimus, just yelling at him. Like, would it finally get through to OP if Bee actually told him he hated him? Just venting all of his years of bitterness and anger?
I think we all just want to see Optimus hit over the head by a clue by four. Do we need to stage Bee's death?
With my understanding/Headcanons of the hate plague, it would ultimately lead to him being attacked. Getting physically violent becomes "irrational" anger, which is when they turn red.
Nobody would know Bee was infected by the hate plague until he turned red-- until then, everyone would just think he snapped.
That being said! Here are the events, in order, that would happen:
Bumblebee shows up, just like in canon, in a spitting rage. He's screaming at Optimus, telling him everything he's ever done wrong, accusing him for his broken sparklinghood, accusing him for never caring.
For just a brief moment, Optimus starts to believe him. Perhaps the neglect really did hurt Bumblebee more than he thought. Maybe Bumblebee really is too young to be on his own.
Bumblebee eventually is drawn to attack - probably from getting into Optimus' face and someone pulls him back, and that's enough to make him snap, because the hate plague really does amplify all emotions to 100 - and turns red, revealing to everyone the nature of his outburst.
Optimus begins to think that all of that was hate plague speaking, revealing deep insecurities and not actually Bumblebee's true thoughts. The hate plague, after all, is known to manipulate emotions to be stronger than they are. Of course Bumblebee was sad about being placed in hiding, but he didn't actually hate Optimus for it. That's ridiculous.
Of course, once he's cured, Bumblebee doesn't admit that any part of it was true, but he doesn't outright deny it either.
Everyone other than Optimus knows it's the truth. They can see it clear as day, displayed on Bumblebee's shattered expression, even as he tries to apologize and claim guilt for the entire situation.
If Optimus does accept his own matter of responsibility in the matter, understand that Bumblebee is angry at him, that he's been hurting for stellar-cycles if not vorns, he would honestly probably.... go off on his own and sulk instead of actually confronting the issue.
I do want to say! A majority of the reasoning for this is because I just like reaaaaally drawing out angst. I don't like it when there's a quick easy solution. I like it when it takes a super long time to fulfill because nobody will communicate, dangit!
I also do not want to redeem Optimus because, while I do believe everyone can be redeemed, I think it makes for an interesting story when not everyone is redeemed.
Optimus is on the right side of the war, and maybe, arguably, a good person, but he is certainly not a good parent.
Even within the show it's shown that he cares for the Terrans more than Bumblebee.
Bumblebee giving the triplets guns within a day of them being born? (Production Bible, I believe, said it was his doing, or at least something he would do.) That's because that's what happened to him! He's been wielding his blaster for as long as he's been alive!
Every scrap of bad parenting on his end was learned from Optimus and I hold to that. He's working on ending the cycle of abuse (he would never abandon the Terrans, never neglect them, could not even fathom it) but it's slow going.
He doesn't fully understand how to be a good parent, but he's learning from Dot and Alex.