I think future humans are definitely worthy of consideration. Consider placing a time bomb in a childcare centre for 6 year old kids set to go off in 10 years. Even though the children who will be blown up don't yet exist, this is still a bad thing to do, because it robs those kids of their future happiness and experience.

If you subscribe to the block model of the universe, then time is just another dimension, and future beings exist in the same way that someone in the room over who you can't see also exists.

I would have to disagree that there is no mediocre way to make asteroid risk worse through poor impact risk management, but perhaps it depends on what we mean by this. If we're strictly talking about the risk of some unmitigated asteroid hitting Earth, there is indeed likely nothing we can do to increase this risk. However, a poorly construed detection, characterisation and deflection process could deflect an otherwise harmless asteroid into Earth. Further, developing deflection techniques could make it easier for people with malicious intent to deflect an otherwise harmless asteroid into Earth on purpose. Given how low the natural risk of a catastrophic asteroid impact is, I would argue that the chances of a man-made asteroid impact (either on purpose or by accident) is much higher than the chances of a natural one occurring in the next 100 years.