Even Yoshida has mentioned, more than once, that Emet's intentions were "pure" and he truly tried to believe in the Sundered again and again, only to be betrayed by them again and again.
EDIT: For clarity's sake, I'm specifically referencing
a Japanese stream in January 2020 where he was a guest and said about Emet-Selch: "You could call him pure-hearted, perhaps... he tried to believe in them as much as he could, but was betrayed countless times, so as a result, he gave up. But he thought [because of Azem/WoL] 'this time, just maybe...' - Emet-Selch held some of those feelings in his heart, as well." (Once again, if someone better than me in Japanese wants to clarify/correct, please do!) He basically repeated the "he tried to believe in them but was betrayed over and over" line in that MogStation talk a while back, when explaining the difference between the Emet we see in Elpis and the one in Shadowbringers.