I see what you're saying and agree that pre-apocalypse, no way Rick would have offered to kill someone's husband. But that's Rick's whole point - you have to adapt to the world they are in now. Rick is doing that. I don't think Rick is becoming what he "really is", he's not a cold blooded killer, but he's adapting the way everyone needs to. The world they're in now has more decaying zombies that try to eat you than civilized humans, so you always have to be on guard. For the humans that are left in the world, chances are they are sizing you up and judging you by what they can take from you (I believe Rick even said this). The two groups they've recently come into contact with - Woodbury/Governor and Terminus - both ended terribly which further proves that. You can't trust anyone the way you could in the world before the ZA, so when a bad egg comes along, you need to eliminate it now before it progresses any worse. Rick realizes this now after seeing the way things ended up with the Governor and Terminus, when they had the chance to eliminate the threats and they didn't.
On another topic, another forum I frequent had a side by side screen shot of the dismembered body Darryl and Aaron stumbled across and the last image we saw of Morgan and they appear to be the same. Did anyone else catch that? I'll try to upload the image later, but it had similar clothing, skin tone, even down to Morgan's wedding band. It would be pretty anti-climactic if this is how Morgan ended up, but it would show us this new group the Wolves (speculation that's what they're called based on the foreshadowing) are bad business, especially considering how hardcore and prepared Morgan always was. I hope this isn't the case though, because I'd love to see Morgan team back up with Rick. Morgan gets it, and would buttress everything Rick has been trying to get across to the Alexandrians.