Why can't the "Enemy Missing" ping be changed visually so it can't be used negatively?
Nobody can deny that the "Enemy Missing" ping gets abused in toxic ways all the time. It happens thousands upon thousands of times every day, where players spam ping their teammates with the question mark ping in a passive aggressive way. This can be enough to set people off sometimes, causing fighting and bad behavior. In order to combat toxicity, we should take away more of the player's ability to be toxic. And at the risk of sounding rude here, anyone who doesn't want the ping to be changed is either abusing it for toxic purposes or simply doesn't like change. These are very bad reasons to keep the ping as it is.
Truth be told while there are many ways to be toxic, making it harder to be toxic will certainly make a difference. There are players who genuinely think "I can't get in trouble if I don't chat, I'll just spam pings instead." Of course while this logic isn't true (Bad actions have consequences and malicious intent is difficult to hide) people still abuse the missing ping and it still causes others to get frustrated, tilted and so on. Believe me, ping spammers have turned matches into a raging wildfire and it'll always happen. Especially due to the power of the passive aggressive question mark. (Side note: Maybe ping spam should be nerfed?)
You might argue that one can simply mute another player's pings, but this isn't a very solid argument: You might miss a valuable ping from that spamming jerk who, at some point, might decide to stop abusing pings. Muting someone in any way, shape or form should always be a last resort due to the fact that muting puts you at a communications disadvantage, which can have game-changing effects if someone you don't want to hear ends up relaying critical information. This is also why players who enter matches and immediately mute everyone can cause lots of frustration, because failing to communicate and cooperate with the team has many consequences.
With all that being said, there is absolutely no good reason not to change the "Enemy Missing" ping to something that can't be weaponized as a tool of toxicity. As for what it should be changed to, unfortunately I don't have any ideas. But I believe that ping spamming, especially abusing the "Enemy Missing" ping makes up a significant portion of toxicity in matches. It's essentially the go-to tool for those moments when players want to be a huge jerk to their team in a subtle way. (Does Riot even see ping spam in chat logs?)