The 4th amendment protects against unreasonable search and seizure. The issue is what's reasonable and unreasonable. Those change with the situation just like what's free speech. You can't yell fire in a crowded theater. You can search a building for someone if you're in hot pursuit without a warrant when under ordinary circumstances it would require a warrant. Your luggage can be opened and inspected by customs without a warrant when you are entering or leaving the country. Your vehicle can be searched when entering and leaving the building. If you're driving across the country they can't search your luggage or car without a warrant (with exceptions)
Another part of the issue is who decides reasonable v. unreasonable, and whether or not there is an obligation to explain the boundaries between reasonable and unreasonable.
If you're driving across the country they can't search your luggage or car without a warrant (with exceptions)
Heheheh - "with exceptions."
Even the 'reasonable' searches require a warrant based on a sworn afidavit and probable cause.
Read the 4th Amendment. It won't take long.