If you are referring to Border Patrol highway checkpoints - DRUGS! These highway checkpoints are "immigration" check points. As a US citizen, you don't have to answer any of their questions as to where you are coming from, or where you are going. US citizens are free to travel in their country without having to answer to the Border Patrol. They have NO authority to detain you for secondary inspection to search your vehicle unless they have adequate evidence that you are violating federal immigration laws, or are concealing illegal drugs. You can always say NO! If you are not violating any federal law, and you voluntarily submit, you are giving up your CONSTITUTIONAL RIGHTS! Just like paying mordita on the south side of the border, doing so makes it harder for the rest of US trying to preserve our Constitutional rights.