The author works for CATO and writes in WaPo.

They think global warming is a minor threat that requires minimal to no changes in regulations, but heat waves (that, according to her, have always been the same every year) are a massive threat to the public and requires immediate changes in regulation.

Because weather engineering is experimentation with potentially huge unintended consequences both for the people in the relevant region as well as people in neighbouring regions and potentially even further.

How would you feel if your neighbour started doing something that was good for them but disastrous for you? Or something with good intentions that turned out to just be a huge mistake causing billions in damages, maybe even lives lost?

Weather engineering is extremely risky, we can barely predict the weather a few hours in advance. We have no idea what kind of havoc we might cause trying to do it on a large scale.

The reason is that one allows you to destroy harvests and ecosystems while the other does not.