This option to exclude spoilers would prevent any message with spoiler tags from showing up in the message search results.
The reason I want this feature is because there are some people who do things like spoiler tag only one word of a message. This could still result in someone having something spoiled for them even without clicking the spoiler tag, because then they'll know what the spoiler is by process of elimination.
Here's an example: https://cdn.discordapp.com/attachments/595810033040752661/644248196058578944/feedback_example.PNG
I know, spoilers aren't 100% avoidable, but I thought this would help a bit.