"No one is advocating that Mr. McKinnon should go unpunished"

Actually a lot of people (in both countries) do share the view that in exposing flaws in these government computer systems he was actually doing the US government a great service, and it ought to be grateful rather than wanting him punished.

It might be embarrassing for the US Defence Department to be shown up in this way, but so what?

As has been pointed out, this figure of $700,000, or whatever it is, is almost certainly made up mostly of the cost of blocking the gaps in security which McKinnon showed up, before someone with genuinely hostile intentions can make use of them.