I always try to scatter my kale seeds (and others) thinly so they don't require too much thinning. I am too impatient to dry a single seed at a time at appropriate distances, so I just scatter lightly. Yet, some spots (or even a whole row) always wind up looking like this (above), lots of little plants growing tightly together.
This makes them more difficult to thin, but that's my karma. Of course, even if I'd scattered them at more appropriate distances, they would need to be thinned. You don't sow kale seed one every eight or 12 inches (recommended growing distance) because you must account for some seeds not germinating.
Thinning plants is rather tedious, and I've often avoided it. However, the thing that gets me out there thinning is thinking of it as a bonus harvest. Clip off the tiny plants just above the soil and you have baby greens -- a free gourmet offering! They can be used in salads, steamed, or stir-fried.
I also harvest the baby winter radish greens, although they grow so fast that they were pretty much toddlers by the time I got to them. I've been using the as my main salad green. Not everybody likes them (they're too much spice and bitter for my husband), but they feel so nourishing to me. Last year I couldn't get enough of the winter radishes themselves, especially the purple daikons, so I'm hoping for a good crop this year. I'm not sure I'll make it through all the radish greens before they get too old if I only use them in salads, so I will try them in stir fry or soup, or just mixed into other veggie dishes.
I also planted collard greens -- a day later than I planted the kale and they are so much bigger than the kale. I've also planted brussels sprouts, for greens only. I haven't ever been able to grow satisfactory "sprouts," but the greens are tasty, especially after a frost. Because they grow more slowly than the other greens, they're still waiting to be thinned... I mean harvested as baby greens. They should make a tasty stir fry.