I generally commute along four-lane 30 mph [50 km/h] main streets. Is this wise?
You need to exercise judgment based on your circumstances.

I generally agree with the advice to ride on arterial roads rather than side streets. But in my own town, there are some arterials I'll gladly ride on, and some I won't go near. There are many side streets that would be slow, with constant stopping, and a couple that are practically bike highways.

So: is it "wise" to ride on main streets? That depends on whether you're trying to get somewhere quickly or want to take it easy. On how fast and aggressive traffic is on the road. On how wide the lanes are.

If you're asking whether it's "safe," that's another question. Bike riders tend to be overwhelmingly concerned about "overtaking collisions," where the car runs over you as it passes you. These are obviously scary. They make up a low proportion of all bike v car collisions, although they do make up the plurality of all bike v car fatalities (although less than 2% of bike v car collisions result in a rider fatality). Most bike v car collisions occur at intersections. If an arterial has fewer intersections along the way, and those intersections are better controlled, it seems that the arterial should be a safer place to ride.