There's no theft: Steem will still exist and so will those tokens. This is a voluntary movement by people who don't want to support the value of those tokens, when they were promised for development and people made decisions based on those promises.

This is one of the true wonders of blockchain technology: it allows people to freely associate, disassociate from those with differing principles, and reform as a group again, all on a voluntary basis. At the end of the day, the value of the coins on both chains will be determined by the values of the supporters of each coin.