Is this a thing any human can really do? I mean, we evolved to quickly recognize emotions in others. I agree that in the context of an Internet discussion, the sensorial bandwith is so low that miscalibration is frequent, and so we should strive to achieve "non empathy". We have though a whole section of our brain devoted just to that, so I guess that this particular bias is hopeless.

You can certainly use the part of the 'empathy' modelling capacity to realise that telling other people what they feel tends to piss people off when you are wrong (and sometimes also when you are right). Failing to adequately account for such likely reactions isn't an inevitability, it is a social skills failure and a fairly blatant one at that.

Most people learn not to do this after embarassing themselves a couple of times when it backfires. (An except is when attempting to deliberately provoke or one-up another ("U mad bro?")).

Is this a thing any human can really do? I mean, we evolved to quickly recognize emotions in others.

We also evolved the capacity to suspect that a thought we have might be wrong, and to develop notions of confidence.

Don't strive for 'non empathy'. Strive for 'not being overconfident'. Also, keep in mind Scalzi's maxim, "The failure mode of clever is asshole"