Nitpick: White House, not Whitehouse.
As others have said, there are controls on the handling of physical documents, but they’re largely trivial to circumvent. And draconian controls on pieces of paper would be pretty silly, since it’s so trivially easy to transmit documents electronically. Short of a strip search, there’s no way to keep someone from smuggling out thousands of documents on a thumb drive.
So, yes, if someone has the proper access authorization*, it is trivial to simply walk out the front door with classified material. See Edward Snowden and PFC Manning for some particularly egregious examples.
Beyond that, though, I think there are some fundamental misunderstandings in play about the “stolen records” in current headlines. Those documents were presumably removed when Donald Trump was still President. This next bit confuses a lot of people, including some people who should really know better.
Under U.S. law, the President has sole and absolute authority to classify, declassify, grant access** to, and control and regulate handling of classified documents. By definition, the President simply cannot mishandle a classified document. This is one are where it’s actually true, if the President does it, it’s not illegal.
The documents in question were presumably removed when Donald Trump was still the President. If they were removed and transported to his private residence with his express authorization, no laws regarding the handling of classified information were broken.
The legal issues around those “stolen records” have to do with laws on Executive Branch document retention, not with their status as classified documents. That last does come into play tangentially, though. Pretty much every administration gets into disputes over whether some documents should be considered the private papers of the private individual who happens to be occupying the office of President of the United States, or official government records. By definition, if a document is classified, it’s an official government record, and subject to document retention laws. The legal issue at play isn’t that classified documents were removed unlawfully, it’s that official government records were retained unlawfully.
*Most of the real controls are on access to classified information, which requires more than simply the proper clearance.
**The President in theory has some limits on his ability to deny access to classified documents, such as due process rights and fair administrative procedure laws when denying a clearance, or requests from Congress for access, but the courts have historically been reluctant to get involved in such cases.