I think that Corbyn is a genuine but fundamentally misguided man, whereas Johnson is insincerity personified, but they are not the reasons I will stay away.
Until manifestos are legally binding, meaning that the winners must put forward bills to try to get them on statute, then they are nothing more than soundbites and sales pitches. Leaders / politicians can go on air and promise the earth knowing full well that they will never have to deliver. There will always be excuses as to why what was promised cannot be progressed - at this moment in time. They are always there for a future that never comes until they are quietly forgotten. And let's not forget the mud slinging, there will be plenty of that as well.
Thankfully there is a documentary on 5+ about the Flying Scotsman locomotive, so I'm good.