No-one needs to justify themselves on this forum.
In the case of persisting with unsupported and vulnerable operating systems that have the potential to disrupt the use of the internet by others, I have to disagree with you on that.
Since no further security vulnerability patching is being done by MS on XP, it must be seen as open season for hackers to exploit any vulnerabilities, whether to create bot-nets or some other means to attack or prevent access to legitimate internet sites - commercial, government or private.
How many people blithely continuing to use XP would have any clue whatsoever that their PC may be being used for such a purpose? Having malware active on a PC is not necessarily apparent to the user. Believe me, the cleverest malware isn't.
I'm not saying that every XP installation will be hacked and used in such a fashion. Nor am I saying that moving to Win 7, 8 or 10 will guarantee immunity.
What I am saying is that wilfully increasing the risk to oneself
and the greater internet community is both foolish and irresponsible.
"Sure, it won't happen to me. I'm so careful / clever / complacent". Famous last words.
FBW