I think my honest opinion of CONCORD is that they are corrupt, at least to some degree. It's not-so subtle when you think about some of the mechanics in game and I think it lends to the belief that CONCORD is at some level, corrupt.
1. a CONCORD agent was working for the Sansha during the live RP events leading up to the formation of incursions. I think it was Rote Kapelle amongst others who killed the CONCORD agent, a little fitting given their Anarchist status (they later fought on the same side as the Sansha to provoke fights). Her being a double agent, and also a long standing double agent lends to the credibility of "if there's one instance of corruption, there is likely more."
2. During the incursions run-up, despite the Sansha stating they were going after CONCORD's ability to prevent them from attacking systems, they (CONCORD) never showed up to attempt to stop them. The most help that was gotten from those early fleets was random live actors for one of the four major factions arriving too late to do anything really important.
3. CONCORD in general allows some pretty shady practices. Like for instance, war decs? Where you basically 'pay-off' CONCORD so you can shoot at another capsuleer run organization? Sounds corrupt to me. Sure some of the oddities are based around "game design" but doesn't make the actual items they support any less strange from a RP sense. CONCORD might not be as corrupt as any of the Empires, but at some level they are still corrupt. For instance,
Security status. Where 'Prison' to amend crimes past equates to going into low/null sec and blowing up pirate battleships for a sec status increase that scales with the ships you blow up. So basically a way to amend is to go kill enemies of the empires and CONCORD. There is no "Pay a fine" option, nor a true secondary option. Indeed pirates in pods can safely traverse all of highsec without incident if they know what they are doing. Hell, if a -10.0 pirate docks in a highsec station and undocks in a battleship, and can make it to warp before the faction police or CONCORD show up, they make it safely to their next jump. Think about how little it would take CONCORD to just be waiting outside of that station, making it impossible for these criminals to escape so easily.
To me, there is just too much evidence that CONCORD is at some level corrupt, perhaps it is because their very mandate is bad, but I find they way too far from being "Overzealous" to let that slide. In fact they aren't really overzealous about anything.