rms famously refused to secure his account @gnu.ai.mit.edu, and so the machine basically became an open shell server for every hacker in the world, ca. 1992.
Lots of hijinks ensued, and it was usually not possible to do anything useful in that account, since it was usually broken or pwned in remarkable ways. But they were wild, fun times.
In a similar vein, EFF cofounder John Gilmore famously refused to secure his SMTP server at toad.com [1]. He believed SMTP should be open for all just like the old days, potentially making it basically an open relay for every hacker and spammer in the world. And so, he got into trouble with his ISP. Gilmore said the server was in fact rate-limited and the abuse potential was not as large as it appeared to be.
Hah! I don't doubt it, but amusingly that section of the article is blissfully free of citations or sources, just some original research. Cool stuff.
I used to do dumb stuff by telnetting to mail servers, back in the day. I think I really annoyed a few coworkers with that; one said he almost called CERT.
I think it was one of the earliest Cybersecurity realizations I had about how insecure the Internet really was, based as it was on blind trust among hosts that were supposed to have legitimate admins in control. I found that it was so easy to telnet to a mail server and feed it whatever you wanted, this must be the tip of the iceberg. And it was!