Yeah, see E. E. Cummings, who wrote his name with and without capitals and his signature included capitals. The all-lowercase version was preferred by publishers for design purposes.
It’s passive-aggressive and control-freakish when you insist that other people must adhere to your idiosyncrasy in their own writing.
Aliases follow the same rules as regular names. User names originate in a completely different tradition in which people generally treat the conventions of writing much more cavalierly. They are not given the same status as a person’s actual name. It took some time before a user sign in name started becoming an identifier, and it still has a large technical purpose that puts it in a different context than an actual personal name.
No, I was merely being careless, which is a common feature of online interaction. If I had thrown a fit whenever someone capitalized my user name in the traditional manner of an actual name, then I would have been precious and passive-aggressive.
I wonder if we’re perhaps reading too much psychological weight into other people’s orthographic experiments. In any case, I’d say it’s impolite to deliberately spell another person’s name differently from the way you know perfectly well they wish it to be spelled.