The hostility is on display right here, just asking how hard it is to use another template engine gets you a "hamlet is the best" response from one of the devs.
Your list of benefits is a list of things you like. Telling me what you like doesn't make it so that I also like what you like. Yesod offers no advantages to me, as I would be using it without hamlet and without persistent, making it just an uglier happstack or snap. As I said elsewhere, I am one of the significant number of people who feel yesod's over-use of template haskell and qq is unnecessary and detrimental. It seems to appeal primarily to non-haskellers.
7+ hours before you posted this an anwser to Agorak's question "how easy is it to switch templating languages?" was kindly given by Michael Snoyman (lead dev of Yesod).
He says: "I don't think anyone's actually done it, because most of our users really like Hamlet. That said, switching should be a piece of cake. All you need to do is [...removed techincal details...]"
I cannot find anything that you describe as hostile.
I think this whole "hostility" thing you seem to perceive is simply not there. Just friendly open source collaboration for the greater good is what I see.
Yes, he posted that after Greg posted "no, hamlet is the best thing ever nobody can want to use anything else". Greg is the other yesod developer/maintainer. Notice other people have replied with similar sentiments. I think your love of yesod is blinding you.
Your list of benefits is a list of things you like. Telling me what you like doesn't make it so that I also like what you like. Yesod offers no advantages to me, as I would be using it without hamlet and without persistent, making it just an uglier happstack or snap. As I said elsewhere, I am one of the significant number of people who feel yesod's over-use of template haskell and qq is unnecessary and detrimental. It seems to appeal primarily to non-haskellers.