I'm of the initial opinion that the passport requirement will have virtually nil effect on reducing terrorism or even illegal immigration given the vastness of the border and lack of security upon it. I mean, it's so easy to get back and forth across the US-Canadian border, maybe even moreso than Mexico, which is already so porous and ineffective that there is no protection there. As with many gun laws, this one--given the factual scenario--seems likely to only affect the law-abiding instead of the criminals who could care less about such laws and regularly evade them. The passport requirement can, however, cause significant inconvenience to the law-abiding. I do believe in holding passports and I hold them and even carry them to Canada although not required to do so, but it does seem to add an extra hurdle that won't advance the ball. I would also sympathise with border residents who will be most inconvenienced, especially with simple things like worn-out passports, damaged passports, forgotten passports, etc. They wear out quickly with use. I can only imagine the hassle it will cause to people like those who live in places like Point Roberts, Washington where the American town is totally surrounded by British Columbia and they must travel around a Canadian peninsula to get American access, etc., snags with the massive back and forth Detroit/Windsor transit, cross-border business road routes, etc.