Sergei
You described MacLover2000 of fanaticism.
Fanaticism can best be discribed by using the following synonyms:
zealot (one who is fanatically committed to a cause) Your right, he is committed to helping other people.
extremist (person with extreme views) Your right, he strongly believes in the ability of Avast! to keep his computer free of viruses.
monomaniac (paranoia; being irrational on one subject) Your right, on occasion Mac gets that way about his Apple Computers.
hothead (short tempered) Your wrong, he usually has the paitence of a Saint.
bigot (a person blindly attached to a belief to the exclusion of all other considerations) Your wrong, Mac makes as many mistakes as any of us do. After all, we are all mere mortals but, he'll also be on of the first to admit that he's made a mistake.
Actually, most of us on these forums fit into those same answers.
Hopefully this gives you a good idea of the type of people you'll find here and we sure would like you to be one of us.
Peace my friend.