1. Chris was a liability. I don't think Tony would have killed him had Chris not admitted that he wouldn't have passed a drug test after they crashed--at least not right then. If Chris was anyone else, Tony would have had him killed instead of sending him off to rehab for his drug problem. He was still fucking up with the drugs and I don't think Chris would have sacrificed himself to do serious prison time if he had been caught. His loyalty to Tony and Cosa Nostra at that point was basically zero. I could see Chris ratting even if he hadn't got jammed up with a case or drugs.

2. Ralph was also a liability. He was plotting to take Tony out at one time and defect to NY as well, those two were on an inevitable collision course. Seemingly from way back. We didn't get the whole back story with Ralph, but clearly there was something else going on there between them. Tony doesn't like Ralph from the time he came on the show. With Ralph close to Johnny Sac before the mole joke, he was doing the same sort of the thing with NY Paulie was. Ralph asked to be put with NY, he threatened to kill Tony in front of Vito and Eugene, etc.