The principal aim of most members of Congress is to secure reelection to office. In order to do this, Congress avoids controversial moral and cultural issues whenever possible. Far better to have the Supreme Court, an unelected body that voters cannot unseat, take the blame for unpopular decisions.
Similarly, the Constitution clearly gives Congress the sole power to declare war. But, wishing to avoid blame should a war go badly, Congress has abdicated its power to the president. It is better, Congress thinks, for him to take the blame for Vietnam or Iraq. By its own lights, the Congressional policy has been remarkably successful. Most incumbents are reelected. The cost, though, is a severe one. Our actual Constitution, one of congressional preeminence, has been replaced by the Happy Convention, in which the president and Supreme Court have supplanted Congress. No Jeffersonian can accept this.
While pointing out the dangers of the Supreme Court and the unitary Executive, a democratic Congress also poses dangers. Repealing the 17th Amendment would establish the Senate as the office that would take responsibility for being the unpopular adult, while making them accountable in a way that judges are not. The Supreme Court is dangerous because it is unaccountable to anyone. A proper Senate would be accountable to state legislatures, avoiding the danger of great centralization of power in the federal government. The 17th Amendment made it more difficult for people to know who to hold accountable for government.
Accountability would promote responsibility.