Most people won’t reveal, and rightly so, what church they go to and attend.....it’s a safety issue. ..and wise to be careful. You never know who is going to get information on you on line.
Denomination is not ‘church I go to’, so that explanation doesn’t work.
One can say ‘baptistic’, or ‘mormonish’, or catholic, Pentecostal, or something. Or maybe independent Baptist...something like that.
And there’s no security issue at all.
The few who did ended up regretting it.
The minute you are labeled and pigeon holed, someone will find the craziest, most whacked out person who they claim represents your religion and try to associate you with it, all based on the alleged fact that they are allegedly part of the same denomination.
And there is the identifying people issue. In some cities where there is only one or two churches of a particular denomination, something like Calvary Chapel, or Assemblies of God, if the person revealed their denominational affiliation, it would not take a lot of work to figure out who they were, and who needs anonymous internet stalkers making their lives hell?
Of course, even that is not a valid reason for some.
I’ve probably given out enough information about me and my location thru the years that a medium sized nuke placed at the centroid of it all could probably take me out.