If only that were true. But I’ve never seen a single mind changed from these online “debates”, because no one ever enters them willing to admit they might be wrong.
Suppose we divide up the audience of a typical debate. (Caveats: people are on a spectrum, it's not likely symmetric, and this is somewhat framed in terms of political parties but shouldn't be and I can't be arsed to fix it.)
Your base agrees with you, and is invested in that position. They're not going to change their mind, but they may abandon you if you don't demonstrate that you're committed. Your aim is to motivate them to support you, through money or activity.
The other side's base is the opposite, of course. And your aim there is to get them to stay home, or to abandon their side. This is why hypocrisy is such a common charge and there's so much focus on various scandals.
Persuasive arguments are aimed at people who haven't formed an opinion. That's why plainly ideological outlets will present themselves as objective and authoritative; people who feel they are neutral can sign on with them without feeling like they're actually taking a side.
So the reason you don't hear people changing their mind is the people who are likely to are those who haven't formed an opinion, and thus aren't sounding off in the first place.
Moreover, the evidence you present is rarely as compelling as you think. Ask a lawyer how often they've had to talk down clients who were convinced they had an ironclad argument. The big ideologies have axiomatic differences they are not necessarily fully aware of, and those tend to be why neither is convinced by the other.
But it is possible to raise a point they have a genuine problem with. If you have done so, the thing to look for is not an immediate response. It's that the other side's talking points shift in response; especially if they shift to "let's change the subject."
