Its got nothing to do with increasing capacity or revenue. The Taylor report required league sides up to now the Championship to become all seater following a number of serious incidents in the 80's not least Hillsborough. It was a far better solution to Thatcher's Government idea of compulsoriy membership schemes.
n my view terraces are fine at our level and a couple of leagues ahead, however once grounds are at capacity the issue of safety arises. I am a Surveyor and have dealt with safety at sports grounds, and safe standing is perfectly possible until a safety certificate is abused by clubs looking for money or violated by unruly fans gaining unauthorised admission. AKA Hillsborough or again recently with Liverpool and Man Utd fans in Europe.
Seating can be an issue, see previous comments from me and the stewards, especially if there is trouble and also if you have to sit close to a dickhead.
Seating also compromises atmosphere as singers can't always congregate together even where clubs try to generate singing areasa, it doesn't allow new fans to join in.