It is true that Garner's actions contributed to his death -- but unless you are an anti-smoking Nazi, his actions weren't putting anyone in danger. He was violating a pretty scurrilous, and petty, ordinance. Yes, as some others have noted - his being out of shape probably contributed to his death, but he wasn't doing anything that required someone to rough him up.
The neighbors had complained about all the cigarette selling in the street. This was community policing, because the cops were trying to clear up a problem that was causing complaints.
The loosie sellers were the thing that brought teenage hoods and bums to this street and attracted other crime. Eric Garner had been cited several other times for doing this, and I don’t know why he freaked out on this occasion (one initial report said he had cocaine in his system, but I haven’t seen that since). He was a big guy, and all they were trying to do was control him.