BuddyPress.org

btw, your plugin here would redirect anybody in any situation to the registration page,… even google etc…

That’s not quite correct - only non-logged-in users are being redirected :p

let people browse your site, they will register if they see fit.

Agreed, partially at least: I’ve been running a BP community a while ago where I used a similar snippet: Guests could browse the site freely as long as they did not try to access members’ profiles. If they did, they were redirected to the registration page. Helped a whole lot to generate registrations - with a surprisingly low percentage of “dead accounts”.