Why?
Because there can be another guy who has tried to make a living from selling a product in the same niche - a high quality product for a reasonable price.
And the 'altruistic jerk' has just ruined the business of the good guy turning the niche into a monopoly of the free crap.
Do you think it is an okay thing, applied to either brick and mortar or software?
No "free" software is actually free. The developers have just used some resources from elsewhere to create the product (spare time while earning a living from a daytime job also counts), and then released it for free gaining an unfair advantage over those who try to make the product development self-sustained. This is purely cheating or predatory pricing.
With this kind of reasoning the person who is pulled into the pile of crap deserves it.
I see lots of free projects that could have made their authors rich, but didn't. Instead the authors keep enjoying their daytime jobs.
Actually, speaking of "deserving the business", the question should be why is the thing free? Why won't the 'altruistic jerk' set a fair price? It may be because in this case they would simply lose the competition, and the only way they can make it is by seducing the customers with free stuff. So who does actually deserve the business and who doesn't?