Why we allow the goel hadam to take revenge could have to do with the issue of whether or not the Torah really thinks that the rotzeach should be patur from an "accidental murder" in the first place. At the beginning of the 2nd Perek of Makkot the Gemara discusses a number of drashot that clarify the definition of shogeg as an accident where there was a degree of negligence-- not a case of ones where it is totally not the rotzeach's fault. The gemara also discusses other "in-between" categories, including "karov l'mezid" and "karov l'ones".
There is also a machloket Makkot 10b about what happens if the goel hadam kills the rotzeach-is he chayav or not? Prima facia this machloket seems to be based on different ways to read the pesukim, however the underlying issue that they are debating could be this very question: Is there a such thing as an "accidental" murder, or is the rotzeach b'shogeg really chayav mitah?
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Tova W. Sinensky
Ma'ayanot Yeshiva High School for Girls
