Then challenge it instead of ignoring him.
I do, but it's a lost game after all. He doesn't care about his writings, I do. He can't comprehend where he's wrong, I'm forced to highlight it. He doesn't syllogize his counter-proposals, I must provide valid arguments to make a point. Now add to these that he's mocking you on every single post.
Does it worth even having a conversation with him? No. Does his opinion affect some people? Can't say for sure, but having him banned from the Dev & Tech board shows me it's disapproved by some mod(s). Is this some sort of limitation of the forum's free speech that I'm unaware? Why not getting him rid for good? Once and for all.
Usually this is what happens to a user who's constantly reported for trolling. (And actually gets his posts deleted)
Let people think for themselves, even if they're newbies being exposed to franky1's posts. You (or the forum) don't need to be the gatekeeper of the truth.
This works oppositely too: Should you leave a malicious user cunningly propagandize against you? Isn't reporting also considered gatekeeping of the truth? All I'm saying is that he gets his posts deleted very often which discourages you to argue with him.
create a solid rebuttal thread with all the LN stuff etc and respond with a link to that thread when he derails a discussion, thus negating his potential negative impact on newbies etc.
That's maybe a smarter, less violent solution.