Well, Bitcoin could probably not reduce this kind of slavery directly, but could reduce the power of certain groups and forces behind the slavery, mainly banks and investment funds, and it also could help lower the dependency of many third-world companies on external currencies (like the USD).
Most companies depend on financing from sources that have only profit in mind and don't care about ethics (or do so in a "marketable" way, like CSR). Many of the employees - even higher-ranked ones - of these investment companies don't have bad intentions but are caught in the system themselves - they must deliver (profitable) results
Bitcoin and cryptocurrencies can deliver a less elitist and more decentralized way of investing. That's possible in the banking system too (there are, in fact, "ethical banks" where customers invest because they know ethics are respected, and even banks with P2P lending) but they are, until now, niche players. And crowdfunding is potentially easier with cryptos than via fiat-based centralized middlemen like Kickstarter, above all, in third-world countries.
On the other hand, a future "stable" Bitcoin could replace the USD and other currencies viewed as "stable" as the main token for accountability in third-world-countries' companies.