Why? Because it's cruel to try to destroy the comforts of other people. Who are you to say they're not enjoying their lives? Maybe that comfort they get from religion allows them to do exactly that. Maybe you'd actually destroy a person's happiness by convincing them their beliefs are bullshit.
If you need to believe in an imaginary sky fairy in order to enjoy our life or stave off your fear of death, you aren't enjoying your life.
At its worse in the past religion has led to those things. In most countries however what remains of religion has become more modernized. Do you fear witch burnings in 2020?
To be honest, um, yeah. The notion that we've become "more civilized" is often an illusion. We are always one step away from the savage, and religion indulges the savage.
One "moral Panic" becomes passe, and another takes it's place. Within my lifetime, we had the "Satanic Panic" of the 1990's.
This wasn't some bygone age, this was 20 years ago, when we had computers and space shuttles and this shit still happens.
en.wikipedia.org