I never argue with people online, rarely in real life too. I tend to listening other's opinions whilst silently judging them. Modern discourse isn't about changing people's opinions, it's about reinforcing your own.
Arguing with people online is pointless. They have their opinions and you have yours. Neither of you are willing to compromise and change your opinion. That would be a sign of weakness and we you can't let them win. You both put your side of the argument forth, slander one another, and both parties come away feeling superiour about themselves. When two people argue neither one really listens to the other person, they just wait for their turn to speak. You might as well be yelling into a tin can trying to get your voice heard.
Online debates are not about sharing knowledge or enlightening the other person to something they may have been ignorant about. These arguments are basically saying "I'm right. You're stupid." Making this statement would be too blatant so we hide our intentions behind facts, anecdotes and persuasive techniques in an attempt to demonstrate - "I'm right. You're stupid." In fact arguing with someone online trying to change their opinion might have the opposite effect. Instead of convincing them you're right you actually just strengthen their belief. This is known as the Backfire Effect -The more your beliefs are challenged the harder you hold onto them.
"When the debate is lost, slander becomes the tool of the loser." - Socrates
Slander has certainly become the tool of the loser in the political sphere. And with Donald Trump president the whole world has lost the opportunity for civil discourse. Prior to the recent Trump v Clinton election most online debates surround politics seemed to be reasonably educated, discussing policy points and the like. Now however it's degraded into a meme war, doxing and threats of personal attacks are common. Neither side is going to convince the other to change their opinion. Its one giant blackhole of intellect, draining the intelligence of all those who engage in the phony discourse.
Changing your opinion isn't a sign of weakness. It's the only thing to do when confronted with new evidence.
When confronted with new contradictory evidence changing your opinion is the only rational thing to do. However somehow it has become seen as a sign of defeat or shameful to be caught changing your opinion. I never understood this, you shouldn't hold an opinion regardless of the evidence, every belief you hold should be open to change if new evidence is observed.
I suspect the negative perspective of opinion changing is related to politics where politicians are labeled 'flip-floppers' if they change their opinion on a key issue of policy. However I never really understood why this is. We should expect people to change their opinion when it is right to do so, actually we should praise them for doing so.
If you continue to hold fast to your opinion despite overwhelming evidence to the contrary then... You're beyond helping.