Do you remember in Stargate when Daniel Jackson proposed that they were the landing pads for alien space ships? Ignoring the part where the Goa'uld turned up and proved him correct, he had a more substantial hypothesis than this. One crackpot on the internet whose idea of a rebuttal is to go "ha!" does not present an effective counterpoint to generations of established Egyptology. The most effective rebuttal of the entire argument is to point out that he's entirely wrong about there not being tombs. We've found the tombs and are indeed still finding them.

Egyptian tombs have suffered from literally millennia of theft and tomb raiding, so it's hardly surprising that there's little to nothing left. What made the discovery of Tutankhamun's tomb so groundbreaking wasn't the tomb itself, but the fact that it was still intact in the 1920s. It wasn't just the grave goods that were targeted either: Felix Bonfils' famous 1875 photograph shows a trader openly selling looted mummies on the streets of Cairo. In fact the sale of looted remains had formed a very lucrative black market to Europe for centuries, as a mistranslation of the Arabic mumiya - a pitch resin commonly used in Persian medicine and as an aphrodisiac - led to a belief that it was either scraped from Egyptian mummies or was in fact made from ground-up dessicated corpses from Egyptian tombs. This trade in 'Mummy dust' throughout the Mediterranean reached a peak in the 15th century before a correction of the translation led to a wave of revulsion and condemnation of the practice, although it didn't entirely die out until the 1700s. By that time, however, ground mummies were also being used as a pigment for paint known as "mummy brown". The Victorian enthusiasm for Egyptology combined with their neo-Gothic fascination with the macabre also made mummies popular items for upper-class amateur antiquarians, and mummy disections were also carried out. Perhaps thankfully, there was also a rapid drive for museums to secure their own collections of mummies and Egyptian artefacts, both to preserve what they could and also to bring in the crowds as public interest grew. Bristol City Museum, for example, acquired the [mummy of Horemkenesi in 1905](https://www.ncbi.nlm.nih.gov › ...PDF The Unwrapping of the Bristol Mummy - NCBI) which has been terrifying generations of Bristolian children (myself included) for decades since, despite in all other facets being a museum of local and civic history and art with no discernable links to Egypt. What this means is that it's perhaps only natural - if entirely gross - that all the known Egyptian tombs had been almost entirely denuded of interred remains by the time they became known to modern archaeology, hence the multiple conspiracies revolving around 'empty tombs'.

The other important rebuttal is that many pyramids are covered internally by extensive hieroglyphic inscriptions which detail the various funerial practices carried out within them.