I think that it is reasonable to assume that since Aragorn had the strength to engage Sauron via Palantir he probably had the strength of will to use it as he wished - especially as he, as king, had the greatest authority to use it, Also it is one of those ambiguous statements since it is qualified by "it was said" ... it is not given as a fact by the author. Rumours tend to spring up about things to which few have access....and it may have been allowed to stand to discourage others from trying to get a peek.... of course unlikely to be a deterrent to small boys who love gruesome things so I could well imaging young Eldarion not being deterred
