OP doesn't appear to be saying Catholicism ought not to grow - rather that they believe trying to appeal to a wider audience than that which is already interested in religion is likely to fail, or worse, backfire.
Religions grow by appealing to a wider audience than that which is already interested. That is precisely how Christianity spread in the first place.
What the Catholic Church is doing is not backfiring even in the terms of the original argument, and I would challenge the assumption that losing people is "backfiring". The church has a duty to preach what it believes to be the truth, rather than what all its members want to hear. Losing some members might not be a bad thing.