>is this legal? or even ethical?

If I ask a public httpd for the content of a URL and it sends it to me, it's my choice to render it how I want. The fact that I might choose to disregard various CSS and overlays and javascript delivered along with the text body content is up to me.

If somebody really wants to implement a fully effective paywall they're welcome to put their content behind a fully active content generated system that requires a unique username/password, same as signing in to an airline's mileage program/ticketing system, your personal paypal account or online banking, etc. Nobody is out there building paywall bypasses that work to render the content of somebody else's Citibank account.