Stop being condescending. The truth will always prevail. Start using simple facts and let them decide for themselves. This is is only way. Those who cannot see, will never see. Move on.
"The truth is like a lion, it needs no protecting. Let it roam free and it will survive."
Can you justify this claim: ‘those who cannot see will never see’? Doesn’t seem true to me. I could not see, now I can. I’ve shown others who can not see, now they can. Have you never known a person who could not see and later can? Seems to be a false claim.
"Those that refuse to see, will never see."
Would make more sense to me personally...
And yes, "refused" would be much more appropriate here but I'll refrain from editing, as the context remains the same.