which conveniently meet the needs of those who quote them, especially Republicans and right-wing Christians
This is part of the "radio/TV talk show" phenomenon. The idea is that a talk show host already has some sort of predetermined judgment in mind. But to keep his or her show popular, he needs to continuously inject new information (news, polls, twitter, etc). Obviously some of that new information will conflict with their predetermined judgments, so they will distort it to suit their needs.
The rationale isn't merely because the host is ignorant; rather, the success of the show depends on its listeners/viewers. And if the audience doesn't like what they hear, they'll just change the channel until they find something else that tells them what they want to hear. So the hosts continually dig themselves deeper and deeper lest they risk their show getting cancelled.
Also, this problem is not unique to conservatives, Republicans, right-wing, or Christians. Liberal groups do this too, most problematically in academic institutions (including top level universities) where the minority conservative thought is often demonized and even censored.
Smart people ignore these types of shows and think for themselves.
is it true that 30% of adult Japanese males buy Junior Idol videos or photo books?
Regarding JI videos, that is blatantly incorrect. If "photobooks" includes regular gravure (and not just JI material), and maybe also magazine stand gravure, it might be more believeable.
More likely the statistic was meant to indicate
a certain demographic of Japanese men (for example, men who consider themselves
otaku, or perhaps single men between the age of 18 and 30, and so on),
but not all Japanese men.