The key difference is that almost all the value of the domain comes from the fact that you have a monopoly over it, whereas that is not the case with stock: I c

The key difference is that almost all the value of the domain comes from the fact that you have a monopoly over it, whereas that is not the case with stock: I can buy an equivalent Apple stock from someone else if I don't like your price. The other aspect is thinking about which activity is actually economically productive. In the case on investing in Apple, you're producing value, since Apple wouldn't otherwise been able to exist without the capital. In the case of domains, me buying a domain in 1990 is completely unproductive (the domain is still "there" regardless if I buy it or not). I don't see the value to society in rewarding people for rent-seeking on monopoly goods, while the value in encouraging capital investment is clear. Capitalism doesn't require this sort of rent-seeking, and Adam Smith (as well as other thinkers) identified (and formulated solutions) this problem in the case of land, which is similar.