There's so many aspects on this topic.
First, that's the point, make a "Discussion" / don't "Argue".
Now if even you making a discussion with your friend, make sure your judgement is valid, maybe he's ignoring you & the fault is yours.
If you guys agreed to discuss that topic, or you forcing your topic down to his throat.
If he spoke his final answer & he's no longer ready to talk near that topic & yet you're forcing.
If disagreed or agreed on something & you pushing yourself to change his mind by force.
If he said he would talk about it later & you trying to take him as your opposition again & makes him like (he's running from you, he's failing ect . .)
Maybe he's just not making eye contact with you or doing some other stuff while you're talking (then that makes you think he's ignoring while he's not! Some people are like that, they listen & do other things in the same time, you need to learn to cope with it)
but if he's ignoring you literally without anything else or misunderstanding involves, then he just showing that he's not willing to make a such a conversion with you so let it go before it ruin your friendship but anyway that would be rude to ignore someone without expressing anything. So make sure you are not misunderstanding by your own fault then make your choice.