Too much of almost anything can be bad for you, that is why it is called 'too much.' That said, they have a high fat content (about 70%) as well as the sodium -- if you have issues such as high triglycerides like I do, you might be more apt to stay away from eating too many of these.
Sodium has been shown to be bad for you in large amounts. Most Americans get more than the RDA of sodium just from the food we eat, it is in canned goods and sodas and all sorts of boxed foods. So if you are eating the shelled ones and sucking the salt off while cracking them then yes it might be bad for you.
Sunflower seeds are a good source of protein though, maybe consider unsalted ?