How do you deal with the problem of the US population becoming more urbanized such that eventually we might have 70% Republican states to 30% Democratic ones? The Senate then becomes a purely Republican controlled one.
That's extremely unlikely, but let's hypothesize a situation in which 70% of the states are rural Republican and 30% are urban Democrat. So the GOP always controls the senate and Dems always control the House. Then you either form something like a coalitional government where both sides have a veto, which in your scenario would be just the status quo, or you negotiate some kind of split.
This would be like the scenario where Lebanon assigns fixed seats for christian/muslim votes.
The issue with geographic states as minorities - as opposed to other minority categories -- say bald men -- is the geographic group is a functioning community and it can secede, so you have to decide whether you want to keep them in the country or not.
This goes back to the original debates in the constitution, where the smaller population states weren't willing to be a part of the country unless they were given a veto.
Nothing about that has changed.
It's just like when you have a team -- 10 developers with 6 feeling strongly to do A and 4 feeling strongly to do not A. Well, you find some compromise where both sides agree, because you if force A, and you do that over and over where the same group of 4 keep having their ideas overriden, then you lose 4 developers from your team. They secede as there is no reason for them to be a part of a team that keeps overriding them, and they can walk.
So if the 70% of your states are constantly having policies shoved down their throats that are extremely hated, then you are going to lose those states.
Now you can say, "no if they try to secede we will crush them militarily" and now the mask comes off that this is about domination and the imposition of the will, which suddenly undermines the whole concern for fairness and democracy.
So you are back to requiring a compromise. If you have 51% of the population, you should get 51% of what you want. Not 100%. And this power discontinuity is a well understood defect of the democratic decison making process -- e.g. it's not representative, whereas a consensus decision making process is more representative. In the consensus process, you give a veto to the minority. Now which minority gets the veto? Well, the founders selected the small state to be the minority because they can actually walk. Not bald men. So due to the underlying dynamics to keep the nation together, we give the rural states disproportinately a bit more power.
