You may have good intentions, but continually asking questions like "What specific law means you cannot do it?" (even politely) is still kind of rude. Who cares why he doesn't want tips; it's his call to make.
But the article I'm responding to doesn't just say "I don't want tips, thanks", it's a long blog post that states quite clearly the author believes nobody can accept tips this way, that Bitcoin is useless, that anyone who doesn't love paperwork must live in a broken country, etc. It's not a simple position statement, it's quite the polemic! Meanwhile, lots of people are tipping each other apparently without problems.
Given this state of affairs, it seems a reasonable question to ask. After all, that's what this web page is for - discussing the blog post.
You may have good intentions, but continually asking questions like "What specific law means you cannot do it?" (even politely) is still kind of rude. Who cares why he doesn't want tips; it's his call to make.