A warming earth is considered bad by people because of the negative effects it will have on people.

Some of the major issues with a warming earth are rising sea levels. This has the potential to displace literally billions of people while simultaneously annihilating large areas of agricultural land. For people this would normally be considered to be a fairly major negative.

At the same time the effects on rainfall, climate and agricultural capacity in many regions of the earth are also at risk of making some of the most heavily populated areas on earth unsustainable in the not too distant future.

We are also seeing what appear to be the effects of more energy in the climate system, in the form of more events and more severe events, most of which are bad for humans.

In theory the warming could make some currently sparsely populated areas more habitable, Eg northern Canada and northern Russia, but these are limited portions of the globe and even if warmed some may not be suitable for human habitation or agriculture on a scale that would replace areas that have become less habitable or productive due to climate change.