Want to go from City A to City B at 500mph? No problem. We already have a complete infrastructure in place that will allow you to go from just about any city to just about any other city at high speed. It's called airplanes and airports and has existed since before you were born.
This method is uncomfortable (legroom), nauseating (turbulence), frequently delayed or cancelled (weather), with inherent capacity limits (airspace, runway space), and long lines for creepy invasive security checks (TSA) before you get on. High speed trains have none of that.
You should try taking a high speed train some time in Europe or Asia. The station is downtown, often right next to your destination or a quick subway ride away. You can arrive 5 minutes before departure and get on with no problems. There is no security check, just a guy at the platform entrance to check that you have a ticket. The train leaves exactly on time and arrives exactly on time pretty much every trip (and by "on time" I mean actually on time, not within the half hour padding that airplane schedules have to boost on-time rates). The ride is perfectly smooth and quiet, often with free wifi, and plenty of leg room. For trips of 150 to 400 miles, it's frequently the fastest option door-to-door as well. Just try this once, and I think your opinion of high speed rail will change.