So a couple of commenters went there: saying that car congestion contributes to pollution and inefficiency, and therefore reducing congestion contributes to my goals (listed above). Superficially, that's true, and that argument's been used many times to get environmentalists to go along with all kinds of shitty road projects. But we need to keep these things in perspective, and that means taking into account other impacts on our goals.
The argument is that cars use gas and pollute the air constantly, so that the longer they take on a given trip, the more gas they use and the more pollution they generate for that trip. Acceleration runs the engine faster, so that stop-and-go traffic uses more gas and pollutes more than free-flowing traffic.
The main problem with that argument is that all of the "congestion mitigation" techniques are complete failures. Widening highways just induces more driving, so that before long the highways are all full. Building transit may take some cars off the road, but that road space is just taken by other cars. The only proven way to reduce congestion is road pricing.
Okay, so what's wrong with reducing congestion with road pricing? Well, it's not so bad if it incentivizes walking and transit use, but not if it simply discourages travel. We want that economic activity; we just want it to happen on foot, by bus and by train. Cars use more fuel and pollute more per person-trip than a moderately full bus, and way more than the same number of people on foot or by bike. Of course, road pricing would also free up space for buses, and increase demand for competing transit services, so that's a good thing in itself.
The overall point is that sometimes mitigating car congestion would contribute to our goals, but not enough to pay too much attention to. In general, it's just not a productive way to think about transit. Car congestion is a problem for drivers of private cars, and when transit planners worry about it, it's a sign that they're thinking more about those drivers than about their own passengers.