[grobdriver]

If the killer did not have access to high-calibre, semi-automatic weapons they might not have exacted such a bloody toll

Reject the premise.
Lack of access will never be possible no matter what laws are passed.

Deal with the perp - not the inanimate object.

[Sherman Logan]

Lack of access will never be possible no matter what laws are passed.

This is not, in and of itself, a very good argument.

It's exactly the same one liberals use to argue against border fences and other attempts to prevent illegal entry.

We can't ever stop 100%, so there's no reason to try to reduce it at all.

By similar logic, we should remove laws against murder and rape. Such laws will never be 100% effective, so why have them?

I strongly support 2A. I'm just pointing out that this is not a particularly valid line of argument.