I don't like secularism because it gives certain types of belief privileges. Religious beliefs are, in some situations, given protection from government criticism because of the separation of church and state. For example, in a secular system government-provided schools might not be permitted to raise matters of religions. In a science lesson a teacher can use the value of the speed of light to indicate that stars are very far away to show that belief in alien abductions is almost certainly mistaken, but they are going to get into difficulties if they use the value of the speed of light to show that creationism is false.

Secularism is a form of NOMA - Non-Overlapping Magistera - it assumes there is a spiritual aspect of our lives which is none of the state's business. However, NOMA is false: religious claims are also scientific claims and philosophical claims, even matters of morality. So, in principle, all aspects of religious belief clash with attempts to teach such subjects and legislate on such matters.

Secularism is also highly undemocratic - if certain beliefs are 'unionised' - sufficiently organised to form large groups then those beliefs get protection from the state in a way that the beliefs of individuals don't.