Honestly, it's sort of hilarious saying this when Christianized Japanese were literally participating in a slave trade with the Portuguese, selling their fellow Japanese into slavery, something which offended Hideyoshi's sensibilities.
Though his main issue was that missionaries were converting daimyo and then these daimyo were giving large parts of their fiefs to the church, which, uh, sort of goes against the whole basis of feudalism. It had nothing to do with the peasants thinking they were "worth anything." based on the fact that the rulers had absolute life and death over their subjects, it's hard to say how many conversions were genuine (and bear in mind that a lot of conversions by samurai were for the trade benefits it brought due to merchants).