Even if you understand the commands, you need to trust the website because a malicious site can use JavaScript to copy something completely different into your clipboard, with a newline character at the end to automatically execute when pasted. (Is the newline exploit fixed in all shells? It used to fail in zsh but work in many others...)
One can also paste into a text editor to verify before pasting into terminal, but what noob is going to know or bother to?
In fact, you should delete the terminal altogether. On a related note, powershell access is considered taboo in corporate environments by IT departments. When security audits are done, you lose a point if powershell can be used. It is in fact considered a hacking tool.
Remember that time, when it was possible for about 6 years to hack into any Linux system (without drive encryption) which had GRUB by pressing backspace exactly 28 times? Yeah, good old times.
Better replace your keyboard everytime you leave it unattended, someone could put a keylogger in it. Don't forget to check for hidden pinhole cameras around that capture you inputting your passwords. Etc, etc. Those even work against an encrypted drive...
A friend of mine once downloaded something malicious to his Linux machine and wasn't worried about it. Then some time later, while browsing his files from a Windows machine, saw it and was like, "hey, what's this?" Oops.
He's a tech savvy guy, so I'm guessing the fact he had downloaded it himself really let his guard down.
Sometimes when I've torrenting from a public wifi I'll get a malicious .scr file - but since I torrent from an Android phone it can't do anything to me.
Except websites can tell what base OS you run using browser fingerprinting. It os impossible to lie aboit your OS because of the differences in platforms.