You are making too much of dual citizenship. In reality its nothing more then paperwork. Loyalty is in the heart and actions depend on honor. For both dual and sole citizens.
So citizenship is just a piece of paper to you? Is it like a sweater that you can put on and take off, it's the person inside that counts? No. It's more than just a piece of paper. It's more akin to a marriage than a state driver's license, for crying out loud. Your cavalier attitude towards the mere "paperwork" that enables you to participate fully in the U.S. speaks volumes and explains your unwillingness to be as strict as possible with who is entrusted with military secrets. That "paperwork" puts you under obligation. So you took the oath of citizenship under false pretenses? Is the oath, any oath, "just words" to you?
The U.S. is first and last to me. All other countries are secondary. If it were in the best interests of the U.S. to destroy my ancestral homeland (England, in my case) tomorrow, I would support it fully. Anybody who can't say the same thing and mean it has no business having a security clearance, as far as I'm concerned. Anybody with a dual citizenship would be less likely to feel the same way. If they did, they would be traitors to their other country, and nobody should trust a traitor, even if that traitor benefits the U.S.
But, and this again proves my point- and I will end here- you write that citizenship qualifies you for such rights as fully participating (lets read that as voting) in a country. That's not exactly true. I don't vote in Israel. And Israelis born in the US don't vote here. There reason is that citizenship is not sufficient, you also need to be a resident.
I am a citizen, live, work, vote and pay taxes in the United States. My Israeli citizenship is manifested by my holding an Israel passport without which I could never travel to Israel as they would not let me out of the country on my American passport alone. At this time, for me, my Israeli citizenship is an issue of paperwork. My affection for Israel would be identical was I a citizen or not.