Is it unethical to teach mindfulness for money?

There are several consulting firms out there that teach mindfulness to corporations as a livelihood. Is it bad karma since they are essentially taking this from the Buddhist teachings, adding their own neuroscience research on top of it and selling it as a product for better productivity and emotional health. On the other hand, many mindfulness centres in the west offer retreats in exchange for "suggested" donations. Does this kind of transaction corrupt the dharma or is it propagating the dharma to a wider audience?