1. He raised issues that need airing.
2. It’s about the principle, not the person.
3. Perfectionism-based criticism (e.g. that he only talked about Americans, or drone strikes on U.S. soil) is a thinly-veiled attempt to discredit the whole venture. He’s not arguing in court of law, but in the court of public opinion, and this is his opening argument. He can stick to a few talking points for now and draw the line here, to capture the public’s attention and not overwhelm. Besides, others who would go further can build off what he did.
4. He can run for President, and this can even be his opening shot. I doubt he’ll win, but many politicians have run for president to change the direction of their parties. And let’s face it: the GOP needs it.
5. He’s a senator, and so of course he’ll grandstand. What filibuster isn’t about grandstanding, in part? One person who gets to bring the entire political process to a grind just so he can be heard? But in America, we eat that shit up. Focus on the message, folks, not the theatrics.
6. I don’t even mind that some have opportunistically rose up to join him when they supported the opposite policies under the last administration. On the one hand, it’s never too late to find one’s conscience. On the other hand, now it’s too late for them to credibly turn back.
7. Nobody disagrees with his main point: that the U.S. has no authority to use drone strikes on Americans, on U.S. soil, who are not engaged in combat. The only disagreements are why this was worth filibustering. I think it was, because it set the precedent, which has been eroded over the last dozen years, that the president’s war powers have limits. The details are almost beside the point. And indeed, most of the (ad hominem) arguments by the war mongers are based on breathless indignation at the mere notion that the president’s powers have limits, and how dare this wet-behind-the-ears, Atlas Shrugged-toting man-child come in here and show us up? But their reaction shows he drew blood.
For what it’s worth, I applaud his efforts.