Eh, I think your co-founder has the wrong attitude here. I edit the copy all the time my co-founder writes. Sometimes I tell him, sometimes I just deploy if I'm in the middle of pushing something out. Building startups is all about iteration. One person sees something from one point of view, the next sees it from another. As each person adds their improvements you get a much better final product - you wouldn't be changing it if you didn't see something wrong with it.

By the same token, I totally accept when the things I've spent hours pouring over get thrown out the door. We recently had a design review where someone said one of the elements I put hours into looked like a 3 year old had drawn it (they didn't know it was done by me, they thought it was outsourced). It was the kind of style I was going for, but that reaction made me realise it totally wasn't suitable for the site. I was a little hurt of-course, made a joke about it and brushed it off. We now have a completely new version of this page that's way better than my original vision.

Wrong response: “You fucking trimmed my copy.” “I don’t want to get mad but I sat there for FIVE HOURS crafting that yesterday, there’s a reason for every word.”

Right response: “I see you changed my copy. What improvements were you trying to make? I felt point x,y,z were important and you left them out. If you were trying to make it shorter, here's a shorter version that includes the more important points.“