Merlin aren't stupid, there's a reason for dark themes, they sell, to the average member of the GP who doesn't visit Towers often and maybe not visited at all, when they book their trip to Towers it will be mainly for the park's newest ride. When someone sees the words 'Psychological' or 'Intense' or 'Fear' to them it can grip the audience, making them want to visit. Merlin aren't the only company who use dark themes either, see most of the latest films. They either have A) An IP or something well-known(See The Emoji Movie) or B) Have a 'dark' theme(See Dunkirk).
Dark Themes are something we will have to accept unless Towers realise another way to market their coasters, for example they've replaced the 'World's First' tagline with 'World Class' for SW8. Which can be seen as a start.
I've said it before but personally don't mind 'Dark Themes' but when you get a whole park which has it's major attractions with dark themes, It gives the impression the whole park is doom and gloom, when they want to advertise themselves as 'Magical' much like Cbeebies Land or TowersStreet.
Bert2theSpark, Your number one person to go to on inaccurate stuff...