Everyone that has ever safety-checked their kids' Halloween candy, and then turned around and encouraged those same kids to suck on lollipops licked by other kids with chicken pox and sent through the mail.
There are also parents out there that, more commonly, organize 'pox parties'- one kid comes down with the pox, and then a bunch of other parents get their kids near that kid so everyone comes down with it at once and then get an immunity to it. Those are also bad ideas. So are the ones for measles and mumps.
Honestly, this is what vaccines are for. They have those. They made them for a reason. You know how your kid will react to the vaccine, or at least you're reasonably sure. You don't know how your kid will react to actually getting sick. For all you know, your kid may react badly to the disease, and then you've got real problems. There is the chance, albeit a small one, that your kid might actually die from it. And let's also note: with the vaccine, your kid does not get sick. Getting your kid sick... gets your kid sick. Which is what we're trying to avoid here, right?
Imagine doing this with a car. 'The best kind of protection against collisions is ramming my car into a tree the second I buy it! Surely I will never crash again afterwards!'
And God help you if your kid actually remembers that lollipop down the road and decides to strike up a conversation with you about it years later. 'I've already had the pox, right?' 'Yes, dear.' 'When was that again?' 'Oh, I sent for this lollipop through the mail that had pox on it and--' '...wait, you did what?' 'Ummmmmmmm...'
Honestly, you baby-proof the house for years, plug the electrical sockets, put the Mr. Yuk label on everything poisonous, and then you turn around and go 'Here, have this mysteriously lightly-used and unwrapped lollipop I found in the mail' so as to deliberately get your kid sick? What is wrong with you?