Reconquista?

Christians are dying out!

Now, Christians are not really dying out, but it is a fact that many Christians are converting to other religions and cults or becoming agnostics/atheists. It is also a fact that most Christians in the Western world are "cafeteria Christians": these are those who are only "Christian" because "that's just the way it is" and not because of true faith.

Are there reasons for this negative development of Christianity in the West?

Of course there is! In essence, there are three groups of people that leave Christianity:

1) the ones who simply do not care about religion & the meaning of life
2) the ones who do feel some need for spirituality, but dislike Christianity for its rules
3) people who are convinced by shallow arguments put forth by scientism

I feel no need to discuss the first group of apostates any further as I deem the description to be self-explanatory.

The second group includes the people who apostize from Christianity and join other religions. The most popular groups Westerners now join would be Islam, neo-pagan cults like Wicca and Eastern philosophies/religions like Buddhism and Hinduism. Here again we can distinguish between two types of people: between those who are sincerely seeking the truth and those who have a sense for spirituality, but do not wish to have the inconvenient rules - especially on sexual morality. People belonging to the latter group normally join Wicca and other neo-pagan cults to still be able to have a "spirituality", but not at the cost of the exaltation of human nature.
People belonging to the former are the ones who join Islam, Buddhism and Hinduism.

The third group of people may include both those simply seeking a justification to live a life according to their personal desires devoid of any objective moral/divine Law, and those who truly seek the truth and therefore start to question religion, in this case Christianity.

What can be done against these tendencies?

There is a solution to these problems: education. Most people who leave Christianity apostize due to ignorance: not only due to their persona ignorance, but also due to the ignorance of certain clerics and their unorthodoxy. When people recieve proper Catholic-Christian education, it wouold be rather difficult to find supposed counter-arguments against the Christian religion.
Furthermore, the lack of truly orthodox Christian clerics and lay members - e.g. religion teachers - also is showing its fruits: people tend to believe that religious pluralism, modernism and relativism are compatible with Christianity, but they are not.

If we want to solve this problem, all we have to do is to go back to true orthodox Catholic education!