What's stopping the downloaded script from wiping my home directory? If you use this, how can you feel comfortable?

You're not wrong, but there's an element of trust in anything like this and it's all about your comfort level. How can you truly trust any code you didn't write and complie yourself. Actually, how do you trust the compiler.

And let's be honest, even if you trust my code implicitly (Hey, I'm a bofh, what could go wrong?) then that simply means that you're trusting me not to do anything malicious to your system.

Even if your trust is well-placed in that regard, I don't need to be malicious to wipe your system or introduce a configuation error that makes you vulnerable to others, it's perfectly possible to do all that by just being incompetent. Or even being a normally competent person who was just having a bad day while writing the script you're running now. Ooops.