Firstly, it presents a chance for Gordon and the party to take a stand on a serious issue of principle with very little political risk attached. The attitude should be: "If David Davis wants a debate about terrorism, let him have one."
The worst than can happen is the part will lose the by-election - which everyone expects it to anyway - but if it's true that Labour is closer to public opinion on this issue than the Tories, they might actually do much better than anticipated.
But there is a deeper, more devious reason why Labour should play along with Davis's game for now - because it is not in fact in Gordon Brown's political interests for the former Shadow Home Secretary's bonfire to be pissed on.
In fact, if anything the Prime Minister should be busily pouring petrol on the flames. The more publicity that Davis's by-election stunt attracts, the more awkward it will make it for David Cameron
I'd even go so far as to say it's a win-win situation for Brown. Either Davis does worse than expected, which will puncture the Tory revival, or he returns to the Commons with a thumping majority to make more mischief for Dave.
It is clear to me from DC's coments about the "permanent" appointment of Dominic Grieve that he does not intend to bring Davis back into the Shadow Cabinet, which is even better news for Labour.
Not only has the Tory frontbench now lost its star performer, but he is set to return as a Michael Heseltine-type figure on the backbenches. Gordon will be a happier man tonight.