Would the opportunities lost be greater than the calamity experienced if the charging of interest was made unlawful? The problem is that man's greedy and envious nature has resulted in the creation of usury and the occurrence of fraud. The poor are not willing to save for the future and the rich are not willing to risk their money without return. The delay of gratification minimizes frivolous buying and the loss of excessive consumption. That in turn inhibits future production, stiffles hiring, reduces employment opportunities and affects the individuals abilities to buy things and the entrepreneur's opportunity to make things.
Historically, the lack of technology limited the alternatives. Contemporally, capitalism is empowered by expansion and growth. Would living within our means affect growth adversely or cause an unpredictable outcome compelled by technological innovation and entrepreneurship. Would the affect be negative or positive? I believe positive because when much is expected the average person complains while the agents of change are motivated.
Can credit be replaced by discipline? Only if man's selfish nature is overcome by stewardship. Does pride make it impossible for the individual to acquiesce and sacrifice? For the most part yes. Does survival make it possible for the individual to acquiesce and sacrifice? For the most part yes.