I'm a huge believer in giving kids unstructured time, so I know what you're saying. But as a mother of four, I'd answer by saying that you'd be surprised how different kids can be. Some kids really thrive on activities with groups of other kids. Of course everyone should have down time, but the ideal balance can really depend on the kid. That said, of course it should depend on the *kid*, not the parents' desires to make sure their child is keeping up with the Joneses in terms of activities.
Each of my older kids is doing three activities this spring (the younger ones do two), and I know that sounds like a lot (in the winter, they just did one each). But they requested all the activities, they really enjoy them, they do them all on Thursday afternoons and Saturday mornings, and they have the entire rest of the week for downtime. Thursdays are a half-day of school in my district (every week), so even with two (short) activities that afternoon they still get hours of downtime on Thursdays. When my kids get home on other days, they always have two hours of playing outside, free play, and having friends over. A grand total of two hours a week of activities really isn't taking away from the far greater number of hours they spend on imaginative, creative, unstructured play, and it's given them great opportunities to discover interests, talents, and passions they otherwise wouldn't have known about.
In any event, of course you're not wrong for putting your kid into every activity that comes your way. Nor is it wrong for a parent to put a kid into a couple activities that are interesting and fun for the child (and sometimes, in finding out what's interesting, occasionally misfiring with one that turns out to have been a bad match ... as long as you don't repeat that mistake next season! it's hard to know what you'll like if you don't try....).