I genuinely don't understand what the writer is trying to do here. I can kind of understand wanting TVs for spreading information (if you ignore that they could easily be used for propaganda), but I can't tell if child-friendly casinos is extremely naive or extremely sinister.
Maybe something got lost in translation? Perhaps the manga is holding back important info to reveal it later on? Either way this is really weird.
Black demon lord is spreading his influence through religion / sect. Do you know how religion spread ?
"Knock knock, do you have a time to hear our lord and savior Black-maou ?"
or
"Praise Black-sama, those who against Him are infidels. BLACK LIVES"
KABOOOM
In instant way, Procell can just crush that religion, but it will cost a big number of human lifes and grow more hatred towards Procell and Avalon. So, to counter religion propaganda, the best way in Procell opinion (or rather... author's opinion) is to make another propaganda by giving people a lot of entertainment. Television is just another media to spread propaganda in much faster way.
Also, if children can be poisoned by propaganda, it will automatically influence the adults to join because adults are easily tempted if they see children loves them.
Children's gambling can not just give them money. Gacha is enough for them. They spend money, play the game, got dolls or toys. That's already a fun way to attact children to do gambling.
In reality, people prefer donate to streamer or buy concert ticket rather than donating to temple / shrine. Or even kids prefer watching Sunday morning TV than go to church.
Psychologically, people will join the cause
ONLY if it gives them benefit or something that they never experience before.