I'm more worried about the 12.1% who declared they are "nothing in particular". IIRC, that percentage has doubled in the past several years and continues to climb.
Check out their method and methodology. It might shine some light no what that statement means. I think it is an interesting statement, but I haven't read what it means in the Pew study.
But to your point, why do you find that problematic? Would a decrease in that response along with an increase in the number of say Scientologists be better? This isn't rhetorical. I'm curious.
Well, Scientology wouldn't be a huge step up, but an erosion in organized religion in general is a troublesome trend. If the % of "nothing" increased to say, 25% in 2020, I wouldn't expect that to be a positive sign of societal health. Of course, one could make the argument that anything other than an increase in their particular brand of Christianity is a bad sign.
I guess I was reacting to my belief that an increase of hyper-individualism in spiritual matters is usually bad. Folks who belong to an organized faith tend to be more charitable, volunteer more, are more likely to take part in social events that assist the poor & neglected, etc. It's hard to help the poor if you aren't connected societally and don't know who the poor are.