Not so. Depends where the big US cities are. There is a correlation (not 100%) between knife laws and open carry laws. 31 states allow open carry now. And for knives, for example in Dallas, Pittsburgh, Phoenix, Salt Lake, New Orleans, etc., you can openly carry fixed blades of reasonable size.
There will always be federal restrictions of course, and some special laws for schools, government buildings, TSA, etc.
The Texas legislature overhauled the Penal Code in 2013 in relation to knives. Now, instead of "
prohibited knives" we have "
location restricted knives". This means that Texans can own and carry pretty much any cutting tool in public except for specific areas such as a courthouse, school, secure area of an airport, Federal buildings (whose rules supersede state law), etc. Private businesses can also set restrictions, such as sporting arenas - most of which now have metal detectors.
Importantly, state law pre-empts county and city level ordinances, meaning that individual counties, cities, municipalities, et al, cannot enact or enforce restrictions that are more strict than state law. That way someone travelling from Fort Worth to Dallas with a bowie knife won't suddenly commit a misdemeanor simply by crossing the city limits.
What if they found out at the entrance that you have a knife? I am not from US, but I am from european country with relatively loose knife/gun laws and the police/security has metal detectors at the entrance to any high level government building, but you just have to hand it to them and they keep it at the entrance (or in a safe). I remember that one of my friends left big Bowie knife in his backpack once, so the police was a little bit suspicious of him when the metal detector found it out, but he had to hand it to them to get into the building, so they let him go. He told them that he cuts apples with it, but who knows. Maybe he wanted to stage a coup d'état that day!
(The open carry is totally different thing. I think that there is no strict law against open carry of knives, even machetes, but the security or police would certainly be interested in you if you went with open carry machete or combat knife where it is kot reasonable - like hospital, schools etc...)
That depends on the situation and the guards you're dealing with. A buddy of mine walked into a Federal building to fill out some forms with a cheap switchblade in his pocket (pre 2013, so still not legal to carry in Texas and definitely illegal to carry on Federal soil). The guard at the metal detector saw it and suggested he leave the building and return after storing his knife in his car. If you're just an average citizen who is obviously not looking for trouble, most security guards will just tell you to leave and come back without the knife. I think they can discern an honest mistake from a deliberate attempt to sneak in a weapon. I have never encountered one who offered to store a knife for me - they just don't want to deal with it. Some locations like football/baseball stadiums even have a locked "donation box" where you basically surrender your knife with no chance to retrieve it.
This is my experience as a Texan, where our knife laws are comparably lax, thanks in no small part to
Critter
. The culture here generally accepts carrying knives and tools (for now). People in other states may not be so fortunate.