My sense is that 'real' voodoo dolls aren't used that way because the magic comes at a cost. It's not just a question of getting the sympathetic ties in place (via body parts/associated items/etc), but that using magic to hurl curses and pain at someone has consequences for the caster.
Of course, magic in D&D has never been portrayed as having that limitation. Here's my take on it, fluffwise.
When you cast a spell and throw a fireball or curse at someone, you're basically using a tool. It's no worse (or better) than grabbing a sword and sticking it into someone's heart. The consequences for the act are no more (or less) than the act itself, plus whatever costs the spell itself exacts.
When you use a voodoo doll, or something similar, you aren't just casting a spell. You are summoning a spirit or minor loa, casting a spell and
giving it to the loa, who then follows the sympathetic tie of the doll and delivers it to the target. You're incurring a debt. You now owe that spirit. And that spirit knows what you did. You can incur judgement in this way, from otherworldly beings. You're involving other creatures in your business. And it may be that the loa needed to carry a higher level spell isn't so 'minor.' And the creatures who are willing to carry curses around aren't nice creatures. And once you get them to START, they may not want to STOP. And you don't give them curses, maybe someone else will.
So once you're on the path of sending pain at a distance, it tends to form a downward spiral, where good spirits condemn and withdraw from you...and all you have left is spirits of madness and pain, and they'll only serve you while you're dispensing madness and pain. And if you stop...then all eyes are on you. If you're riding that tiger, do you dare let go?
This is not to say good or neutral casters can never use these items. It's just to say that when you use them, you're taking risks and opening yourself to the kind of scrutiny normally only clerics are under. When you send a curse to the governor of Nassau, you can't just make a die roll and decide if he lives or dies. Someone else is involved. You have to ask, "Who is carrying this spell? What does it think of this? What's it going to tell its buddies?" If the governor is really asking for it, maybe a decent spirit would be okay with it...such a curse might fall in line with the natural order of karma; the cosmos striking back against the evil he's done. But it's not a guarantee. Sometimes good loa won't do such things no matter what...for reasons mortals can't easily ken. The spirit world is not our world, and has rules we know nothing about.
So to put it another way; the use of narrative weapons like voodoo dolls opens you to narrative consequences that are in many ways subject to the GM's whims and the demands of the story.
Oh, and yes. There's countermeasures. I'm sure any competent practitioner can cast a spell/bargain with an entity to gain protection. At minimum, a Protection from Alignment would generally work...MOST curse-carrying is done by evil critter (or if you're evil, by good critters). Longer lasting protection can be had as well via more powerful spells and/or rituals.
I'd still probably want to adjust my domain spells as I level up if that's okay, to be less overtly offensive. Subversion tactics, that's the rub.
). Once assembled, the voodoo doll might allow attacks/spells used against it to damage/effect the target...not sure what the range would be yet.
