Then we are probably dead anyway, the onus would have been on them to contact us as they are probably several centuries more advanced. In that case its like going with a tank to an island population that still uses bows and arrows
You do realise that comment supports strongly the dark forest theory right? The best thing do do before you have a tank is to shut up and hide. Of course you don't pick fights when you could get squashed
Implied was that the actions to take if we had full info are obvious. If their capabilities are known you would not have to resort to "shoot first, ask later"...
But the dark forest theory suggests when you have an arrow, you should shoot others, because they can have an arrow too. This strategy can go wrong if they have a tank. And if you systematically shoot everyone, you're systematically looking for a tank.