I disagree, there are instances where having a completely different website for a smaller form factor is beneficial to the user.

It is! And I wish more sites would make it accessible like it used to be by just going to m.domain.tld rather than user-agent sniffing, because I often prefer the simpler mobile version I get when I spoof my user agent from the desktop.

Which is great.. until I do a google search for my closest movie theater on my phone to pull up the listings... the link to that theater's page is right at the top... "great" ... now I click the link and the site redirects me to m.theater.com/ (no path after the slash) ... now I'm stuck slogging through several pages to get to what I wanted.

This happens a lot.. there's a page on the desktop site that doesn't correspond. Responsive design still shoves a lot of extra resources at a client that the smaller devices especially don't need. Responsive rendering then loading an adaptive client in the browser is a better option... browser sniffing is the only way to do this.

A phone-optimized site will have less content, usually, so why send the extra data to phone that don't need it, especially when those phones are running at lower bandwidth and are often billed per gigabyte?

I usually find it frustrating when a phone site doesn't let me see what the desktop site does. If there's content only for one form-factor, load it with AJAX.