1. Religion and religious people have the propensity to hijack state laws and replace them with their religious laws. Challenging relgion keeps this in check.
Although we are currently seeing this in the north with Sharia laws being institutionalized.

2. Religion slows the flow of critical reasoning that leads to progress. This is because religion is often conservative hence will always prefer to maintain status quo. It's immune to change, even progressive changes.
Example is with vaccination.

3. Religion is invasive. It doesn't tolerate differences, it thinks its opinon is the ultimate whether or not evidence supports it. Anything that doesn't promote verification of claims should be challenged because such institution if given a chance then it could be a free for all.
Imagine if everything we have achieved as humans was only based on just claims without evidence? Can we even achieve anything?