Involuntary manslaughter, while often times an accident, should be punishable by law. That being said, the punishment for an act that is generally accidental should be significantly less than that of a murder or manslaughter charge. Perhaps a short stint in jail, mandatory volunteering, and personalized public educational segments could ultimately prove to be a just sentence for involuntary manslaughter. The primary reason for a lawful punishment is to help the person being punished to fulfill their duties to society, and the sentence mentioned would allow people to do so.
The law should spell out what people's duties are as far as being careful to avoid harming or worse killing others. Then if they aren't careful and there isn't some reason why they couldn't have been careful or had to take an action usually considered too reckless (i.E. A drunk driver who had to drive because he was being chased by a man firing a gun) then they should be punished accordingly.
There may be cases where no care would've prevented the accident or the care that would've prevented it would not have occurred to anyone except perhaps a small minority with special knowledge (beyond what an activity requires). In that case there should be no penalty.
Yes, involuntary manslaughter should be punishable by law, because the person who is being punished still did something poor that caused the action to happen. Even if a person did not intend for the harm, they still made a poor choice, by driving too fast, or by doing something else that put a person in harm's way and then killed them.
Just think about it, involuntary (dictionary definition: done without will or conscious control, or done against someone's will; compulsory) and manslaughter: the crime of killing a human being without malice aforethought, or in circumstances not amounting to murder. This means that it isn't the persons fault if the victim died. Its like trying to sue the government of japan because your brother was killed in a tsunami.