Though a Buddhist, Asoka promoted secularism. His message–carved on pillars–is summarized in his own words.
Respect others’ religion and they will respect yours. If you have the right to practice your religion, others also have that right. We have many religions, because men have varying desires and passions. But in essence all religions are the same. Hating other religions shows a lack of faith– you fear for your religion. You harm your religion by criticizing others. Honor other sects, and you increase the influence of your own; denounce others, and you diminish the influence of your own.
The message of all religions is the same: self-control and purity of mind. If you inform yourself about other religions, it will open your mind. You will see the similarities and lose the hatred within you. Living in harmony is good for you. This is what I do: I honor all religious sects, ascetics and laymen with reverence. I listen to them. I give them gifts. But I consider that to visit them in person is more important than any gift.