in "Q Who?" the Borg do actually cut through the Enterprise and kill a chunk of crewmen.
No, they cut into the Enterprise
and take a core sample of the ship. The fact that there are people in that core sample is of no concern to them.
They're doing it to study the technology.
Actually, this assertion, at least, is false. The Borg speak only once in the whole episode, and say [according to http://www.chakoteya.net/NextGen/142.htm
WORF [OC]: Captain, we are being hailed.
PICARD: On screen.
(An interior view of the cube, all girders and scaffolding)
PICARD: This is Captain Jean-Luc Picard of the
BORG: (many voices speaking as one) We have analysed your defensive capabilities as being unable to withstand us. If you defend yourselves, you will be punished.
The Borg lock a tractor beam on and begin to drain shields. Picard orders phasers fired to resist and try to terminate the tractor beam, which fails. Then the Borg punish them, as promised.
There is no reason whatsoever to suppose that the Borg are addressing anyone except the crew in that dialog, and every reason to assume that they are, given the fact that the ship was hailed and evidently standard communications signals were sent to the Enterprise