Campen: Seriously, I think this guy's proven that - if nothing else - he isn't a very good fit for the ZBS. If they plan to keep it*, he absolutely has to go, and they need to bring in someone who's got cred at running it. Personally, I'm with the crowd that wants it scrapped - it doesn't fit the personality of the team - too finesse, and as pass happy as they like to be, it's not a good pass blocking scheme. Really, though, I can't see how you can make much of a case for Campen deserving to stay.
Slocum: This will fall into the category of outright rumor-mongering, but I'll go ahead, with the caveat that I have no proof whatsoever that it's true - let's just say it's something I've heard. I have a friend who lives in GB and claims to know one of the (possibly former) assistant coaches for ST. According to this rumor, Slocum got the job over another, more-deserving candidate because he's McCarthy's bo-bo. In other words, total who-you-know/good old boy shit. Again, I have NO proof that this is true. What is certainly true is that ST have done anything but improve under his watch. Certainly injuries have played a part, but even when that wasn't an issue there were lapses and the group was under-performing.
Overall: I look at it this way: When they saw that the D was turning into an anchor that threatened to weigh the team down, they went out and got a proven, top-tier defensive coordinator. The defense has been a strength since. So to me, it makes sense that they should approach the o-line and special teams coaching the same way: Go out and find the best available guys, hand them the reins and get out of the way. McCarthy is human - he has strengths and weaknesses, but the man can coach up a QB and he can put together a hell of a gameplan on offense. He also seems to be able to delegate effectively, at least if he knows he's putting the work in capable hands (like Capers'). So I say give him a couple more pairs of capable hands on o-line and ST.
As others have illustrated far more elegantly than I could, if you want a team that is consistently competing for the division (and in this era that's really the goal - compete for your division and the playoffs on a consistent basis - many of us recall the pre-free-agency days a little too vividly, and that skews the view), you need consistency in terms of the head coach and GM/organization. Players will come and go - you can either go headlong after every free agent star and maybe get a couple good-great seasons at a pop, but you'll be down more than you'll be up, because there's no base on which to build. McCarthy isn't any more perfect than any other HC, but he's stable and certainly a lot better than many other teams' HCs. Thompson likewise has his flaws, but all I need to do is look @ guys like Tramon, Sam Shields, Bishop, Zombo, etc. to see that he and his staff have a good idea for talent and filling the team's needs with guys who can play, whether or not you know their names. That's right out of the playbook of teams like New England and the Steelers, and I think they're good examples to emulate.
Sorry - too many words. Bottom line: I do think that it makes sense to upgrade at the coaching for o-line and ST. They're perennial under-achievers, and certainly in the case of the o-line there have been more than enough players brought in to suggest to me that the issue is coaching.
*the reason (IMO) they went with this is that if it's properly executed you can get away with less talent @ running back and smaller O-line players. The problem is that it's never properly executed, and they have a few players who aren't really good fits for the scheme.