Part One: Social entrepreneurs — those who try to tackle major social problems such as poverty and disease while generating revenues — are often well-meaning people. But in their desire to make a difference to society, they sometimes fail to subject their ideas to rigorous tests. Ian C. MacMillan , a professor of management at Wharton, and James D. Thompson, who leads the Wharton Social Enterprise Program, have just published an ebook titled, The Social Entrepreneur’s Playbook , to help entrepreneurs do just that. In the first of a two-part interview, MacMillan and Thompson explain why it is important for social enterprises to subject their beloved notions to tough love. An edited transcript of the conversation follows. Knowledge at Wharton: To begin with, please talk a little bit about the work that both of you have been doing with social entrepreneurs for the past 13 years and how that led to the writing of this book.…