The OK hand signal becoming a hate symbol was first orchestrated by 4chan. It was a deliberate attempt to appropriate the sign and give it negative connotations as a sort of internet hoax. Take note of the closing sentence in that picture:

Leftists have dug so deep down into their lunacy. We must force to dig more, until the rest of society ain't going anywhere near that shit.

Basically, they were attempting to take that well-known, much beloved, iconic hand symbol and force it to become a source of outrage so that it would stoke the fires of people who feel that outrage culture is going too far.

The idea that we live in an over-critiqued, politically over-correct time is a familiar feeling to many. It was my internal response when I first heard about the hand sign being racist, as I watched one of my coworkers approach another about his use of it. You express the disdain directly in your post. Unfortunately, you, myself, and many others got played in this particular instance (and probably many more). We fell for a misdirection that caused us to direct our ire at people we perceive to be hypersensitive killjoys, rather than the actual instigators of the whole thing, which was the entire point of their "operation" in the first place.

The people spreading this misinformation were directly attempting to raise instability and social friction and make people who take things seriously look ridiculous in the process. The average, everyday person is likely to think that the OK hand symbol suddenly becoming racist is a far overreach, so it's the perfect icon to falsely appropriate for hate. But, of course, it's all just a joke too, so anyone who takes their actions rather than their misdirection seriously is also ridiculous. "Can't you see how absurd this is?", they'll say. "It's not even real!", they'll tell us.

It's a setup entirely designed to avoid responsibility -- a way to have one's antisocial cake and eat it too. The whole point of being edgy is flirting with things that are known to be subversive or offensive, but they also want the safety of disavowing this the moment any actual subversion or offensiveness occurs. They retreat to their castle of absurdity -- the innocence of intent.

There's the idea that a lie, told often enough, can become the truth, and that seems to have happened here. Because their hoax was believed, people then started using the hand signal as a symbol for white power genuinely and unironically. The false pretense of its origin has become overwritten by genuine use. It moved from the purview of anarchic internet mischief into real-world significance, yet they will still try to claim it hasn't by retreating back to absurdity. It's their only move, and as the symbol has gained traction with actual white supremacists, this rhetoric looks even more foolish than it did at the start. You called the mass murderer a "dumb fuck" for using the hand symbol in court, but you should know that that is playing right into their narrative. You're pushing his use of it back to meaninglessness and irreverence, when there's nothing meaningless or irreverent about him at all. His intentions were real; his actions were premeditated. He planned the attack out months in advance. He strategically posted his manifesto online in advance of the shooting and livestreamed the whole thing.

This is not meaninglessness. This is horrific, calculated, ideologically-driven violence. The people running the hoax and seeding doubt across the internet want us to believe his use of the hand signal is meaningless because it absolves them of their flirtations with and provocations of dangerous beliefs and people.

If you want to be mad at someone for the OK hand symbol being racist now, be mad at the people who ruined it in the first place. It's not tainted because some touchy leftists overreact to everything but instead because some other people thought it was fun to play at "ironic racism" like it's a game that's at all possible to win. At best, they're just doing it for shits and really shitty giggles. At worst they're doing it as cover for actual racist or violent beliefs. The only people who benefit from us evaluating which one is truthful is them. If you want to be mad at someone, be mad at the people pissing in your pool and then playing mind games to try to make you think it was someone else, or maybe just a joke.

They want you to focus on why they did it, but why it happened is far less important than the idea that nobody should have to swim around in piss.