Javelin, NLAW and AT4 launchers are for sale by Ukrainian arms dealers. Ukrainian generals and soldiers are underpaid and sell US and UK weapons on the black market. Every wannabe terrorist can now destroy civilian aircraft and kill hundreds for just $20k.
I'd be careful before I believe someone who thinks the Javelin/NLAW/AT4 are MANPADS and that MANPADS pose any danger to airliners. But alas, confirmation bias is a powerful thing.