First off, this is not a scare tactic or a cautionary tale of Taken - type events. This is a conversation about visas.
There are many organizations such as World Wide Opportunities on Organic Farms (WWOOF), or WorkAway that provide wonderful opportunities to volunteer abroad in exchange for free room and board. A couple years ago Jacob and I used WorkAway to spend a month in Sweden, working in a seasonal cafe in the countryside and staying with a sweet family with two small children. We loved our experience there, and as travelers on a tight budget, were thrilled to spend nearly a month without spending a dime.
Some friends of ours, however, weren't nearly as lucky in their experience volunteering abroad. After connecting with a host family who needed help in Scotland, they purchased their tickets to Great Britain with plans of volunteering for 6 weeks. They were stopped at customs in the UK, detained, interrogated, then placed on the next plane back to America - all for attempting to volunteer without a work visa. To top it off, they are now banned from entering the United Kingdom for the next 10 years.
I agree - it seems like a rather harsh reaction to a bit of innocent volunteer work. The issue is however, that with employment rates down and the open migration and work policy of those who hold an E.U. Passport, Europe (and subsequently, Great Britain) is fighting hard to keep employment opportunities solely for their citizens. Even if you are not intending on being paid, these strictly enforced rules can make volunteering in Europe difficult for those with an American passport.
(So what was the major difference between my experience and our friends? Simply put, Jacob and I both hold E.U. Passports, so we were able to neatly sidestep the whole issue.)
Don't give up on the idea of volunteering abroad however! The story ends happily for our friends, who wound up volunteering for a castle-owning host family in Ireland and had such an amazing time they extended their stay.
The point of the story then, is not to skip the idea of WWOOFing or WorkAway, but to make sure you are fully informed. In my experience, the U.K. is the most difficult country to enter under these circumstances (Jacob was even interrogated as a student entering England on a study abroad visa), though many countries in Western Europe enforce strict rules as well. Once you have settled on a country in which you want to volunteer, do some research into their visa policies, and how strictly they enforce rules regarding unpaid work. At the least it will save you from breaking into a cold sweat at customs (always suspicious looking).
Have you had a great (or awful) experience volunteering abroad?