I don’t think legitimate issuance for educational demonstration purposes is a problem. I do live issuance during talks about Let’s Encrypt to show people how the system works.
Please be aware of the rate limits, which will limit your ability to repeat your demonstration frequently:
Also, if you just want to show people how browsers respond to certificates with problems, you don’t necessarily need to create new certificates. There’s a really excellent site that does a better job for that
It’s deliberately created sub-sites with many different problems in the certificate and HTTPS configuration, so that you can explore and test how browsers will treat each of these cases. For example, https://expired.badssl.com/ has a deliberately expired certificate, while https://revoked.badssl.com/ has a revoked certificate, https://wrong.host.badssl.com/ has a mismatched subject name in the certificate, and so on.