You're painting "MBAs" with too wide a brush. There are MBAs in marketing, MBAs in health care, MBA software engineers, MBAs in consulting, MBAs in advertising, MBAs founding companies, MBAs in production and creative fields, MBAs in media, etc.
"MBA" is not a job title; it's a degree. I think the term you're looking for is "finance" or "Corp Dev," which is more of a specific job role that often fields MBAs to fill it. Their job is to get the most favorable terms possible in a deal, but not at the expense of the deal itself. So yes, go into a deal with a finance or corp dev person with your eyes wide open -- but they lose more than they gain if they develop a reputation for completely screwing people over again and again. It pays to know what their incentives are, how their firm makes money, and what your alternatives are to a deal with them (and often, your alternatives involve deals with other finance types).