Come on think about it on any writer's point of view? Do you really think you will attract someone writing for your website without some kind of compensation/benefit in return? You won't, and even if find a interested person to write for your website I doubt that he will even be creating good quality content in your website. You are taking the time and ideas of that writer you should not take advantage of it and make him compensated for that, it's either that or you just start writing articles for yourself.
Yeah, the only benefit I could see for writer doing gigs for free is to build reputation (as I did 20 years ago for a local newspaper), but that implies the site/service/company in question has a way to provide exposure to the writer. Best portfolio for a writer is his work published and online. I'd say putting it on a bad site with no credentials is actually worse for the writer.
OR if the cause is something the writer personally believes in, and is non-profit.
OP: you've seen the opinions. Your response?