What about the poor and minorities? College should not be the only route to a middle class life. There should be opportunities for those that are not academically gifted. Additionally, if public schools failed to prepare lower income students to be prepared, that's the problem that needs to be addressed.
We should also outlaw all GPAs across secondary and post-secondary schools. It should be pass/fail only.
Are we saying there's not enough room in public universities to accommodate everyone? There seems to be enough room in secondary schools, and those should have a much high operating cost per student (buses, lunches, etc).
You mean the SAT? The problems with using a single exam as the primary criterion for acceptance is going to be basically the same as the problems with using the SAT--the scores are going to be very heavily correlated with how much money parents can throw at exam prep.
Either public schools are teaching enough for college level work, or they aren't. You can't have it both ways.
Do we have to continue the traditional college model? Why can't you pay for a class, and have, say, up to a year to finish it without penalty? That would allow people to learn at their own pace. If after the first year, you're not done with your classes, then maybe college isn't for you.
about 70% of US high school students currently enroll in college.  of those, about 60% graduate in six years.  multiplying these two fractions together yields <50% of high school students graduating college in six years. so without drastically changing the current system (or accounting for choice of major, admittedly), it seems fair to say that the median high school student is not actually capable of attaining a bachelor's degree at a typical university.
do we have to continue with the current model? perhaps not, but my intuition is that allowing people to "learn at their own pace" would be more expensive per student. this is just based on my experience as a TA; it is far more work to grade assignments that aren't due on a predefined schedule. to what extent, I am not sure; TA time is not exactly expensive.