There's a difference between not ignoring someone and giving them a platform. As was recently pointed out, Oprah learned that the hard way when she once had Klansmen on her show to "debate" and "expose" them, and just ended up promoting them by associating them with a world-famous brand (her own).
It is why Richard Spencer was worried about the Nazi Punch. He and his ilk were excited at the prospect of being able to appear in public and essentially be given a legitimizing platform by not being treated with hostility. As just another group expressing their views.
It is the reason Westboro Baptist Church often makes national headlines for a moment whenever they go protest, but they're not commonly invited on every major talk show to hear their interesting perspective. And the few times one of their representatives were, absolutely nothing of value came from it (other than the lesson learned to not do that shit again).
I will admit that what's going on here with Milo is probably part of an organic process. Every time this situation comes up, people must decide whether someone or some movement is worth taking seriously, is legitimate. The very arguments over whether or not to give Milo his platform are part of the process. After the Maher appearance, it looks like a lot more people decided "no this is trash". And now, there is this.