I don't think its you asking that question
, but the answer I believe (for pre-clearance in general) is that:
1) If there is a problem with an inbound passenger, they are bounced before they leave the departure airport, rather than being a problem for the US Government; and
2) Relieves some immigration congestion at US arrival ports.
Patriotic Americans shouldn't have an issue with it - its extending the boundaries of US Sovereignty! (One you go through US Pre clearance, you are on 'US soil' - er, 'US Carpet'. )
Once I had cleared US immigration at Calgary airport. We boarded, then the plane went tech, so we were offloaded back to the departure gate. US guard person sat down beside me and said that she hoped it wouldn't be long. I asked any special reason?
"More for you folks. After pre-clearance you have to depart within XX [I forget - 90?] minutes. After that you have to go back."
"Go back?"
"Yes, you have to re-enter Canada through their immigration, then pre-clear US Immigration again before you board."
"Gee, that would be a hassle" I replied.
"Yes" she said. "Especially considering this was the last flight out and all the immigration folks have gone home". :shock:
We got out OK.