Those who do not want Religion to be mixed with governance and politics propagated Secularism.
This kind of Secularism was interpreted by the Theists as Atheism.
The Tamil Secularists, as an assertion denied the factoring in the role of God or the use of religion in political matters. This was interpreted by the Religious/ Theists as a Denial of the existence of God.

Just as kids in the primary classes are taught that the THE SUN RISES IN THE EAST, THE SECULARISTS LEADERS TAUGHT THEIR CADRES THAT GOD DOESN’T EXIST. What they wanted their cadres to learn was THAT RELIGION SHOULD NOT BE MADE A BASIS OF POLITICAL DECISION MAKING in a Democratic society.

Now when people go to Kalignar’s resting place and conduct religious ceremonies, those Believers/ Theists are contemptuous of the Atheists turning to God, after the death of their leader. The Theists probably believe that those Secularists should continue to say that THE SUN RISES IN THE EAST and not that THE EARTH ROTATES TOWARDS THE EAST ON ITS OWN AXIS WITH THE SUN IN THE CENTRE, even though they have come of age!

How ridiculous, that a Believer / Theist instead of being happy that an erstwhile unbeliever has turned to God, are contemptuously looking down on them for backsliding from the earlier beliefs held by those Secularists! Probably even gloating that finally “they succumbed to Religion – like us”!
Why not we look at it like this: After all, in Death no one can be certain as to what happens thereafter.

There were these Pharaohs who were interred with their personal belongings, in the hope that they may need those belongings; there was this Alexander the Great who piled gold coins in his father Philip’s grave – so in Death, why take a chance? At least in the life after, the man may not be assigned a not so convenient place for the sake of not having asked some Cosmic consciousness! It is a practice In Catholicism for the relatives of the dead to pray for the dead for mitigation of the punishment in the afterlife, called “indulgences” even without the consent, when alive, of the dead.

Therefore, I am of the firm belief that the Belief of a follower ‘following rituals and practices’ in the grave for the benefit of the dead, need not be in keeping with the beliefs of the dead.

Therefore, the clamour of those Theists who want to hold those Secularists responsible for their word, in the literal sense, is neither reasonable nor giving them the Liberty to change their minds and beliefs.
No Mortal can be a Custodian of any belief in God, as any Mortal has the Liberty to assert/affirm his own beliefs, but can never “rule out” any other mortal’s beliefs. All mortals are limited by Time and for all we know, may not carry his consciousness beyond his Death.

In a gist, Secularism is merely not mixing Religion in politics & governance and has nothing to do with their personal practices in their Private lives.
Let us be sane enough NOT TO JUDGE THE DEAD. They are beyond the grasp of the Living.