You need to keep an open mind. Your note is a perfect example. People watch many videos every day and some skip videos from time to time. Some will find it interesting, some will not be in the mood. Some might give it a pass. Asking them not to subscribe if you don't like science videos puts people off. People should to your channel to know about things and develop interest towards it. That's the only way to get new crowd. You need to be more welcoming. Not even discovery channel would say that. Even in Youtube, there are many science channels that provide information but good entertainment value.
PC gamers have a saying. We were all n00bs once. It means even the enthusiasts were clueless about how to play or how to get things done when you start. So you have to make up your mind and device whom are you going to make this content for. Is it for enthusiasts who most likely subscribe to popular science channels, forums and websites? Or people who are interested but don't want to be intimidated in the initial process. Take your time travel video for instance. The future explanation part was spot on. The video was enough to explain how you could 'travel' to the future. The past? Not so clear. It was based on theories and pictures.
Next to your video, youtube recommended this:
https://www.youtube.com/watch?v=pQC3ErD1YwE
It was a better explanation. It also used movie references because people who may show interest science most likely are fans of science fiction. I did not graduate in a science field, but I loved the explanation of the future. But not the past. This was addressed by the video as shown above. Understand what kind of audience you want to attract.
Rest depends on your plans.
