I agree. I used to travel a lot and at one time had two passports (from the same country). This was when visa processing could take substantial time for some countries, and so you might not have a passport for travel if you had only one. It is a little unusual, but my government had a process to follow and provide justification for your need. I also cleared it with the country I was living in at the time as a PR, and they were fine with it. There was never a problem coming in and out of the US (naturally, I used the same passport in and out each trip, although not the same passport for different trips). A German colleague had three passports (he was a really heavy traveller) and would visit the US frequently, he had no problems. OK, we weren't US LPRs but I hope this story indicates that the border systems are pretty smart, at least for the US and the countries I was going through. Dual nationality is not an uncommon thing either, and will have been met many times by the immigration staff.