The same way you change anyone's mind about something -- education. Not everyone's opinion can be changed though as some people are just set in their ways regardless of facts or evidence (or the lack thereof). Take the religious for example. Despite how much of a convincing argument you make you're very unlikely to change their mind. Someone who is so against cyrpto for whatever reasons is also unlikely to change their mind, but it can be done via education, especially if they're intelligent and open-minded. When telling people about bitcoin don't ever sell it to them as a get rich quick scheme because that always sets off alarm bells and scares people off, but explain both the positives and negatives and the risks and rewards and let them decide for themselves whether it's something they want to invest or get involved with, but I don't think bitcoin is very everyone so take that into consideration.