The problem with "likely to have negative externalities" is that if you ask whether something has negative externalities, the answer is always yes.
If you carry on breathing, you're emitting CO2 and remain in competition for scarce resources with anyone else who is still alive. If you take your own life you're wasting the resources society invested in your education and causing work for emergency services. Both doing and not doing anything has negative externalities.
One of the things that has negative externalities is accounting for negative externalities. It has transaction costs and compliance costs and enforcement costs.
This implies that there is a level of negative externalities where the cost of preventing them is more than the cost of incurring them. The key is to catch the breakeven point and not go too far in either direction.
The problem with climate change is not living things breathing. It is the insertion of net new carbon into our carbon cycle by digging it out of the ground and burning it.
Not so. You ate food to make that CO2. If you had buried it underground instead, that carbon would have remained sequestered instead of reentering the atmosphere.
It's a good example precisely to show that you can spin anything into a negative externality by comparing it to some possible alternative which is better on some possible metric. Then if you want to show that the other alternative is worse, choose a different metric. No thing exists which is more perfect than all other things across all metrics.
If you carry on breathing, you're emitting CO2 and remain in competition for scarce resources with anyone else who is still alive. If you take your own life you're wasting the resources society invested in your education and causing work for emergency services. Both doing and not doing anything has negative externalities.
One of the things that has negative externalities is accounting for negative externalities. It has transaction costs and compliance costs and enforcement costs.
This implies that there is a level of negative externalities where the cost of preventing them is more than the cost of incurring them. The key is to catch the breakeven point and not go too far in either direction.