Where do people who publish "free proxies lists" get their lists from? I know those lists are commonly used for example by so called "internet marketers" for scraping websites. Search for "free proxy list" if you don't know what I'm talking about. Do people who publish them scan for misconfigured routers so that they can use them to proxy their traffic?
How many percent of those routers you think are home routers? That would be unethical to me because you basically hijack somebody's connection and slow it down for them and just leave the vulnerability for other people to exploit (who may do worse things than innocent scraping of websites).
Furthermore, would it possible to reach the IP owner somehow and inform them about the issue? If that's a home router, would writing to the ISP who may then contact the subscriber and help them work?