You know that the preview text is decided by the sites? Facebook, Google, whoever, aren’t choosing what to display. They’re taking the stuff explicitly formatted as “please show this to make our link more attractive”. (See opengraph)

As AI summarizers of pages really emerge this will be a more valid point, but using the preview text the authors (using a very clear format for that sole purpose) asked you to to allow users to link to their site fundamentally cannot be stealing.