Well, by this logic, then
Buddhism poses a threat to
Christianity in
America, where countless people call themselves
Christian because they celebrate
Christmas and might show up to
church on
Christmas Eve and
Easter Sunday. By the logic the original writeup was describing, these people are
ripe for
conversion and need to be defended from such, except that Buddhism doesn't appear (at least to me -- I'll admit I don't know as much about it as I should) to have an
incentive toward
proselytizing.
I guess the question here is whether the author feels threatened when people who only have a religion-by-default, without knowledge of what they think they believe, are taught about another belief system, and find it more attractive than the empty shell of a religion they claim. Note that this argument can just as easily be applied in the United States or another majority-Christian country to Christianity as the "empty shell," and another religion with proselytizing beliefs (say, Islam) as the teaching base.
But yet, as a Christian, I don't feel threatened by Buddhism, Islam, Jainism, Judaism, Hinduism, Mormonism, agnosticism, atheism or any of the other beliefs I've encountered among my friends or acquaintances (my high school academic team my senior year consisted of a Jainist, a Muslim, a Jew, and little old United Methodist me). But maybe that's because (a) I've been exposed to all these different beliefs and have done at least a passing amount of research into most of them, and (b) I know what I believe and am confident I can defend it to my satisfaction when others attack.
I can't compel people to believe something, or even to educate themselves about something before they discount it. I can try to provide such education, but people have the right not to listen (and believe me, a hell of a lot of people exercise that right). And that's fine by me.