So, if I say I’m a catholic but don’t believe in catholic doctrine, I can be catholic too?
Don't be hasty, though, you might enjoy one of the tens of thousands of names non-Catholics have come up with. You might, for example, enjoy calling yourself an Emerging Homo or a Nondenominational Evangelical Fundamentalist more than you would enjoy pretending to be a Catholic.
But why stop with calling yourself something someone else already uses? Start your own church with a nice new name and maybe you can get enough followers to have your own mega church one of these days.
Something like, "Conservative Evangelical Pentecostal Self Interpreting Contraceptors", would probably draw a crowd so take you time and consider all the possibilities before you bother with pretending to be Catholic.
The people that poll are Catholics, baptized, Catholics that identify as and know that they are Catholic, that is why they tell people that they are Catholic, regardless of the last time they attended church.
Protestants in regard to voting are a much less vetted category.
If you identify as a Christian but aren’t Catholic, then you are put into the Protestant category, even having never been baptized or having attended any church or ever having been a member or identified with a church.