Why do people get offended when we prefer to call the servants of God slaves of God?

I mean like if i say IM PROUD TO BE A SLAVE OF GOD. Why do people frown as if it's sooo inappropiate. Everyone is a slave to something right? a slave to money, a slave to sickening desires, a slave to bad music, a slave to their own life, their job, their community in which they live, a slave of their own doings, a slave to the devil but when we say we are slaves of God, people get offended and say theat's wrong to use the word "slave".