I've never been to a church service.
But, I don't think you can wear jeans or sneakers, much less a t-shirt to church. It's disrespectful.
Then...the pastors are being disrespectful?
It's not really taking the religion thing seriously. Look at Jews, you got your tefillin, your tallis, your tzitzit, your yarmulke. Or Muslims, they have the red-dyed beard and that prayer smock thing. Or think of a nice restaurant even, those require a suit jacket, forget basic semi-formal attire. It's a show of respect to wear special clothing.
Reform Judaism largely dispenses with the goofy garments. I presume there is some sort of liberal Muslim analogue. And many nice restaurants no longer require the stuffy attire. People who live by all these uptight rules are so boring. Live your life how you want to live it.
I've only been to mosques in America and Bangladesh, but in my experience dressing up to go to the mosque does not happen except on holidays. If clothing is appropriate for prayer, then it is appropriate to wear to the mosque.