You have to consider your motives for wanting to share your position with others. You could argue that inappropriately attempting to explain your position in a time of grief is the very same exploitation that religious people are guilty of, using the grief as an opportunity. If nobody has asked you for your opinion then there is no need to give it, you have no duty to try and save their soul like religious people claim to have.

I would argue that the main purpose of trying to convince religious people that they are misguided is to make the world a better place, undermining the beliefs that a terminally ill person has that is a comfort to them is going to achieve little I think. If someone asks you for your opinion by all means give it otherwise let them get on with it as you are doing. I feel it would be much more productive to have such discussions at more appropriate times, Don't expect people to think rationally at a time of grief, that is exactly why the religious people use it as a way to convince people.