For home games I sit in posh-ish seats. I like to see the game from close to the half way line, I don't enjoy singing much. Most of the people sitting around me were sitting around me when the team were last relegated from the Premier League. Prior to the clappers the only time fans in this section sang loud and proud tended to be when people in other sections walked out early when the team were losing to the likes of Tranmere. "Loyal supporters, clap, clap... clap, clap,clap" was as loud as it got.
Clappers encourage people to make noise. When there's noise, people in quieter areas feel more confident singing along, so more people sing. The blokes behind me have started singing. They get the words wrong, but they're having fun. They used not to sing songs with profanity in, now they sing some of them and just leave the rude words out or add a different word. The people next to me clap along to everything. The pensioner in front is often given a new clapper for the second half by the young blokes a few seats down who don't use theirs because he breaks his with excessive clapping.
The clappers work. They are not compulsory, nor is singing or standing. There is more than one way to support the team..