Virtually every website out there today uses Javascript.

Most of those work without it.

Lemmy uses Javascript.

Lemmy is one of several ActivityPub-capable applications. You do not need to use Lemmy inside a web browser in order to participate here. In fact, you don’t even need to use a web browser.

The Web generally does not function without Javascript today.

I disagree. Some websites (with lazy developers) work less well without JavaScript. You’ll gain less annoyances (no JS = no pop-ups and no sophisticated anti-adblock techniques), more speed, less energy consumption, less potential security risks. You’ll lose… not really much. “Web applications” (usually worse, slower and less reliable than installed software), a couple of websites which are very focused on providing effects over contents - sounds like a fair deal to me, but again, YMMV.

Yes, there will never be absolute security. If it runs on a computer, it most likely has security flaws.