I personally hate Chute killers so will kill them in their chutes if I see them doing the same. If I see someone killing chutes I'll make sure everyone in the area know it. Don't get into a big open channel radio argument, just make sure that they get their fair returns.
Other than that, the only time I'll consider killing a chute is if they are stupid enough to pull the chute while still 10K+ in the air. You're probably doing them a favor by doing that, they'd be hanging up there for 15 minutes otherwise. Typically they do it to spy and call 6 for their buddies. Either way they make themselves fair game, even then I usually don't blast them though.
The only other reason to kill a chute is to be a scorepotato. So, if you bail, open your chute at 2K feet and someone still comes down to shoot you, they're pretty obviously a scorepotato. Let everyone know who it is and they'll get their due.
The lesson is, don't hang in your chute too long, open it close to the ground, practice it in the TA just like anything else. The chances of someone blowing all sorts of Alt to come down and pick u off while you are only 500ft from the ground is pretty remote. If they do I'd chaulk it down to a poor pilot who would trade alt for a chute kill. They got their points when you bailed, I don't think they get a bonus for not letting you live to reach the ground.
Sometimes it's just bad luck... HiTech got me the other day but I don't think he really meant to... I had to give him a razing though

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Soda
The Wrecking Crew