Secularism means “I tolerate you”. Which automatically implies you are superior and the other (the one being “tolerated”) is inferior. It’s like saying to your spouse “I tolerate you” (instead of I love you or I respect you). It is like telling the guest sitting next to you at the dinner table, “I tolerate you”. The idea of secular society is thus built on a very fragile foundation. In such a society it is even a taboo to bring up your faith at the dinner table (let alone the other persons faith). It is like walking-on-egg-shells. In fact, its very concept is hypocritical.
Pluralism is born out of mutual respect. In a vibrant pluralistic society people do not walk-on-egg-shells, but share and celebrate and respect each others differences (their faiths, spiritual traditions, etc), making for a more rich and colorful society with great synergy. For example, the hundreds of faiths and spiritual traditions within Hindu culture each have their own set of spiritual sources, books, sages, names/forms/expressions of God, that can be dramatically different from each other, and yet they celebrate and respect their differences.
Pluralism means respect for the other tradition/path just as you would respect your very own. Which automatically implies no attempt to convert. Else the respect is not genuine.
Every modern nation is now only coming to realization that in a world that is shrinking, pluralism is necessary for a sustainable society, and are moving away from the failed concept of secularism and towards pluralism.
Illustration 1: Hinduism
A person (to whom god is Krishna, with their own set of sages, spiritual literature, stories, and of form of God) and a person of dramatically different faith (to whom god is Shiva, with their own set of sages, spiritual literature, stories, and form of God) will celebrate each others festivals together as if it were their own. Hindus celebrate Krishna Jayanthi (spiritual traditions centered around God as Krishna), Navaratri (spiritual traditions centered around God as Durga), Shivaratri (spiritual traditions centered around God as Shiva), Ganesh Chaturthi (spiritual traditions centered around God as Ganesh). A Hindu may go and visit a Shiva temple for spiritual inspiration in the morning, and then in the evening seek inspiration from the words of Krishna. In fact, even within a single Hindu family, you will likely find each persons preferred choice of deity, guru, spiritual practice, spiritual literature, etc all different from each other.
Over time all these different spiritual traditions and beliefs develop tremendous synergy making it seem like “one religion” despite the fact that the differences between each spiritual tradition is far more than any similarities. They each have their own vast storehouse of spiritual works produced by their own great yogis (sages, philosophers, and enlightened masters). It accounts for Hinduism’s never ending stream of spiritual expressions steeped in spiritual wisdom in the form of puranas, epics, arts, music, dance, literature, philosophy, yoga, languages, mathematics, cosmology, metaphysics, etc.
While the faiths, spiritual traditions, schools of thought in Hinduism differ dramatically, fundamentally they all embody the philosophical and metaphysical concepts in the Vedas. It is only the mode of expression that makes them different. Note that while acknowledge the validity of the Vedas and are living embodiments of core concepts, they are not based on the Vedas, and in fact do not even require its existence (albeit only in concept). Many are independently developed traditions, which through different spiritual paths (the many schools of yoga, samkhya, tantra, siddha, etc), have independently affirmed what is said in the Vedas regarding the nature of the cosmos and our place in it (including pluralism which is stated in the Vedas as: “the Truth is one, but the paths are many”). Examples are the Tamil works, Saiva Siddhanta and the Thiruvaaymozhi, giving the same validation as the Vedas.
Illustration 2: Christianity
Christians often give the argument that their religion is also very diverse. That they have numerous Christian denominations.
This is not a valid comparison because you’re talking about diversity within a particular spiritual tradition (that of teachings of Christ). In Hinduism there are many completely different spiritual traditions (each with their own spiritual source, books, stories, sages, forms/expression of God, etc). Each of these spiritual traditions within themselves also have diversity, with far more differences than one would find within different Christian denominations.
If within Christianity there were a number of faiths not based on Christ or his teachings, and not based on the Bible, and Christians respect these other paths as they would their own (even if it is not based on Christ or his teachings), then I’d agree to the diversity. But that is not the case, as all the Christian faiths, are strongly predicated around Jesus, the Bible, and Biblical stories (Book of Genesis / Adam and Eve, etc.), and share the same symbolism (the Cross, Jesus, Mother Mary).
Illustration 3: Alien Civilization
As another example, if an Alien civilization practicing pluralism met a Hindu, then the Alien would say to the Hindu:
“Hey, what makes our [alien] culture great is the amazing diversity, richness, and acceptance of each other… and we see that similar unprecedented pluralism in your culture. For all practical purpose in many aspects you are of our same culture. Where we are different is in our deficiencies, but there is not a culture that doesn’t have its set of deficiencies that it is grappling with, and that shouldn’t overshadow the great strengths of our culture, even more so when the particular strength is something as important as pluralism.”
And the Hindu would reciprocate saying, “yes, I agree, and likewise for all practical purpose we consider you ‘Hindu'”.
But the Christian fundamentalist cannot say that, because the Alien culture does not follow the Bible or have Jesus as their prophet/savior. In fact, the hordes of Christian fundamentalist denominations would see this as a great opportunity to go and destroy that Aliens culture and replace it with there own, starting with targeting the most vulnerable parts of the society (as they cannot coerce those who are already well off). Like a virus, it looks for a weakness in the body, and then from there starts spreading and consuming the host body, without any consideration or sensitivity that it is causing harm to the body (even causing violent spasms in the body). Helping people in need is good, but not at the expense of uprooting pluralism and replacing it with a fundamentalist (and inherently intolerant) ideology.