So the real issue isn't whether a marketing person should come from sales - it's whether the marketing person understands that their job is to actually help sell things. My definition of marketing is "profitably solving customer problems" so - baked in there - is understanding the customer and getting paid. The worst marketing people are those who feel very removed from the fact of the sale. Said another way, the best marketing people are those who understand their customers, do everything to deliver a product, package, price and promotion designed around them - and feel great driving revenue. Someone saying yes by buying is the ultimate validation of good marketing.
Marketing isn't simply an activity. It is part of driving to an outcome and that outcome is a sale.
Most marketing people I know didn't start their career in sales, so I disagree with the premise of the question. :-)
Obviously marketing feeds sales -- whether "sales" are human beings or self-service -- so it's helpful to know what "sales" means. But a career is not at all needed.
I have seen great marketers come from product and technology. Completely agree with Jason about the faulty premise of this equation.
Agree with Jason. The premise of this question is flawed. Marketing is multi-faceted and I've seen successful and amazing marketers come out of lots of different disciplines with varied backgrounds.