There are many reasons that you shouldn't do this. For one, its spam and is considered rude. People will get annoyed at you, and you can get banned from places. Its simply not good manners.
Thats the ethics side of it, but theres more.
This won't actually help you. Yes, maybe one or two people might subscribe out of pity or to "support" you. But do they really care? No. Just because someone is subscribed does not mean they'll watch your videos. Subscribers don't equal views. Those "supporters" will likely never look at your channel again, and will just unsubscribe later when they clean out their subscriptions. This will actually hurt you, as youtube will see this as your audience not caring about your content. Subscribers are actually useless to some extent, they don't really matter. You should be focussing on views and getting people to watch your videos (and watch them all the way through). That actually matters, and will help you. YouTube will see that and see it as your content doing well, and will spread it to more people.
So focus on making quality content that people will actually watch, subscribers will come on their own, and you're much better off growing naturally.
A couple specific tips for you, work on your thumbnails and fix your banner. It will look so much better and will help you a lot.