I was wondering this as well, and also if it was "evil" form to consume souls already in jars. Unless I am missing something, and maybe voice acting would give some indications the text doesn't, it seems unclear to me what the difference is between breaking or using the jars either.
And if source vampirism IS "bad", then perhaps they should provide some other means of destroying the damn "invincible" enemies with a "holy" method. Maybe something related to bless? Maybe you have to sacrifice a source point, instead of gain one. Nothing should be invincible though, really disappointed "galvanized" made a return, so more options for this would be good for gameplay and roleplay.