Secularism is simple, People of all religions, race, sects, genders , languages, Economic status and cast are equal in front of the constitution and law. No discrimination....period.
Any decent educated modern individual should agree to the above. If Zakir Naik considers himself and his religion to be superior to all others then that’s no problem at all, the problem starts when he wishes others to keep him and his religion in a higher pedestal than their own, to enact laws to further this belief, to look down upon other people and influencing others in his community to discriminate as well.
If he believes he can do all this living in a secular democracy like India then he is mistaken, so it’s obvious he had to leave this secular country to preach what he believes.