Gates come in many different forms. Some are physical and some are social. In the realm of the physical we have normal gates which lead into yards and other enclosed spaces. Also there are logic gates of the electrical kind as we see in computer microchips, which can be said to serve as filters in many cases. As for the social, it's quite possible that some people fail to notice them since they are much less apparent than the physical kind of gate. A good example of a social gate is the publishing world where certain ideas are allowed entry and where other ideas are suppressed, not based on merit, but based on how appealing they are to the gatekeepers. In the last few decades there have been more and more options when it comes to publication of ideas and the gatekeepers have been scrambling like crazy to gain control of those venues so that they can continue to suppress some ideas and to promote other ideas.