It’s not mindless trust in authority, it’s recognizing the fundamental differences between Senator and Representative.
The latter is supposed to represent the people themselves, the former is to represent the States-as-institutions.
Which they do with or without the 17th amendment in place. There's a reason why Representative Sheila Jackson-Lee of Texas will NEVER be Senator Sheila Jackson-Lee of Texas -- the state of Texas as a whole has a completely different political ideology than the people of her district. With or without the 17th, she has zero chance of becoming a United States Senator.
That being said, the 17th amendment leaves it up to all Texas to determine who represents the interests of their state, but the abolishment of the 17th amendment leaves it up to an elite few authority figures to determine who represents the interests of their state.
The question is thus whether conservatives feel individuals of a state or the political elite authority figures of a state are better suited at determining their state's relationship with the federal government. Those who hold the latter view oppose the 17th amendment, believing that a select few authority figures holding power in their state government can be trusted more than we the people as a whole to decide their state's relationship with the federal government.
The people of the states are “the states” as far as I’m concerned. The state governments can go to hell, most of them suck, even the GOP ones.