The problem with carbon offsets, entirely depends on how they are used. When carbon offset money is given to a local project, but many try to buy an area from locals entirely. Kenya currently hosts 11 glaciers within Mount Kenya national park.
The problem is that, many of these projects require a rainforest to be left standing or something similar. Without buying from locals, and an income from the carbon offset to support the people who will loose access to the resource, it is highly unlikely that the deforestation rate will fall at all.
Much of these offset programs are being set up in Africa, on a continent which has the least responsibility for climate change, and yet local people are loosing the rights to land that they have lived on for millennia.