I still think that they had 100% decided on having the romance between Debra & Dexter happen. I think they thought they could pull it off, then saw how horrible of a reaction the idea got from the fans, chickened out on it and then they scurried to find some quick fix and end the show. Somebody probably higher up told them to drop the Debra/Dexter love story by fading it out.
Bottomline: The writers are hacks and who ever is in control has clearly given Michael C. Hall too much creative control or control in general.
Basically Seasons 1, 2 and 4 are great with Season 4's last episode feeling like the perfect ending for the series. If you took Season 3, kept the same characters and rewrote alot of it, you'd could make Dexter into a great 4 season series. The problem with Season 3 is trying to have Miguel Prado as a "Big Bad" and The Skinner was such a poorly fleshed out character and basically an afterthought. On Season 3 they forced the badguy role onto Miguel in such an unrewarding way. They should've made The Skinner a more diabolical character and kept Miguel as a friend to Dexter while revealing that Miguel did have some anger issues from his childhood or whatever. I think Dexter and Miguel could've been at odds at the end in a more creative way. To me, Season 3 would've been more interesting had it ended with people feeling satisfied that The Skinner was killed and saddened by what happened to Miguel, instead I ended up feeling the Skinner was a joke that was casually wrapped up too quickly and Miguel was handled poorly just to provide a cheap swerve to the audience.
The whole "Big Bad" thing is what killed alot of the vibe of Dexter. It makes sense that he tracks killers but it doesn't make sense that every other person he meets just happens to be a killer. Now we're at Season 8 and EVERYBODY is a killer even Debra. It wouldn't surpise me if next episode Jamie & Harrison became the first ever Baby Sitter & Kid killing team.