Hit the bullet points.
* In all honesty, I had no idea what the 17th Amendment was off the top of my head. It's not exactly one of the "big ones" talked about in history classes. I had no idea that state legislatures voted for Senate until pretty late in US history. I always assumed it was a direct vote.
* As far as how it hurts the country, it causes federalism to override state's rights.
* State legislatures were able to elect representatives that more closely aligned with overall state interests.
* Today, we see our Senate elections as more national races. We have a Senate race in my state this year. Almost all of the issues talked about mirror what we hear in the presidential election. If it was a vote via the state legislature, the campaign on candidates would reflect more issues closely related to our home -- i.e., how we would like the federal government to fund various programs and the like.
* This would in turn make the Senate more responsive to the needs of the state.
* Congress had the intent of giving the people a direct voice via the House of Representatives. The Senate-via-legislature essentially placed a check of sorts on the whims of the people. It increased the states' power.
* Without that state power, federalist politicians now have almost zero check on the interaction between federal and state powers and rights.