Sorry for all the posts, it took a while to catch up to this conversation 
My perspective is that through your paid, career-path-following day job work you can help the world through design, in consultancies in particular.
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focus on medical or social products that provide benefits for people (for example: diabetes products are huge with consultancies).
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Find the causes yourself, define a problem, and build a business case around it for a firm/corp to spend the time - PR/Corporate Social Responsibility are good business cases that don’t require profits
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do it on your own. Find a problem and a way to support yourself doing it. Doing good work, and promoting it when finished would be career building
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Inject your social ethics into projects. Designers refuse to work on weapons, smoking products, or (sometimes) products they find objectionable. If there’s a problem, you have the option to leave as Yo said.
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As a designer you can champion features for environmental or socially responsible reasons in products you work on
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