Would you do it?

The ethically sound decision is obvious. The consequences of that happening is interesting thought experiment though.

As it happens, it's estimated that around half of the population of Europe died due to the Black Death in the 1300s. That had massive and long-lasting effects on society and the economy. Since labour was in such short supply, serfs were able to leave the land they were legally tied to and find alternative employers who paid them more, so it effectively ended the mediaeval system of serfdom and that led to the development of ideas about how all people should be free. It also had a major impact on religious thought, since the Catholic church had clearly been able to do nothing to stop what was perceived of as the wrathful judgement of God. It even had an effect on fashion: since wages went up due to labour shortages, the poor dressed better, and their "betters" had to wear increasingly elaborate clothing in order to distinguish themselves from their social inferiors.

It's impossible to say what effect a similar cull of humans would have today, but it's very likely all sorts of unexpected consequences would follow.

One thing is sure: the Earth as an ecosystem wouldn't miss having to deal with a drastically reduced human population.