Curious, if I visit the site in question using lynx/links am I still in the wrong?

At least with lynx/links, you don't get any javascript functionality and the experience as a whole is diminished.

With an ad blocker, you selectively block the javascript you don't like but that the operators rely on to bring in revenue, while still getting the otherwise 'full' experience.

If sourceforge went under, do you think I'd be unable to get the source to tmux?

Since obviously I'd still be able to get tmux, what value is sourceforge actually providing me? They might be providing tmux developers some value, but they aren't providing any value to me.

I value what these sites are giving me, but not enough to put up with ads. If adblock didn't exist I'd probably visit places like sf or youtube a lot less.