Either humans are or are not contributing. If we are, we should do something about it. If we are not, and we do something about it, what do we really lose? Sure, there is an economic cost, but there's always a cost for a disruptive technology or fundamental industrial change.
In short, there's no good reason not to do something about it (where as there are an enormous number of effectively NIMBY reasons which are extremely selfish).
We've become a species intent on making decisions that are current, rather than visionary. It's a shame, and it may be a massive evolutionary failure.
I think it's very doubtful that the presence of 7 billion humans on the planet with all their activities of urbanisation, covering large areas of ground with concrete and tar, agricultural practices which tend to strip the soil of its original carbon content and reduce the biodiversity of the soil, and major deforestation that takes place to clear land for agricultural purposes, and so on, could have no effect at all on climate.
The problem is in quantifying the effects on climate that each of these human activities might have and in determining the interaction between the effects of different activities.
For example, the negative effects of deforestation must be at least partially offset by the positive effects of increased CO2 levels, since it has been established with a high level of confidence that elevated levels of CO2 have a fertilization effect which greens our planet and increases crop growth.
Rather than demonising CO2, a more economically sensible approach might be to improve our soils by using no-till farming practices, return the unused biomass of food crops to the soil which effectively sequesters carbon in the soil, and to plant more forests, which should thrive in the elevated levels of CO2 (compared with preindustrial levels).
In other words, we should use CO2 as an asset.