You can delete your posts manually; Bitcointalk doesn't have a "delete user" feature.
Or did you mean he can edit his post? Because no user can also delete post. But a post can be edited to del and also be reported to moderators for a moderator to delete it. But the post can not be deleted/removed by the user. Or probably it is a typo and you meant can't delete.
I think you can delete your personal posts on threads after 24 hours but cannot delete a thread you create yourself and that’s what I thought he meant.
The reason why is that I asked how could I pay with my Bitcoin and which taxation would be applied.
I got a response from an user as if I was trying not to pay taxes and elude my tax responsibilities.
I’m worried someone can legally attack me and sue me because of financial misdemeanor.
If it is about privacy which shouldn’t be a thing too much to worry for you since you didn’t share some personal details about yourself, I would say apart from using TOR browser you can as well create another account as that is permissible when it has to do with privacy issues