If the world was full of folk like you, the likes of Richard Reid would never have been stopped. Just what would it take for you to intervene? A murder?
I think you are being a little unfair on Tezzer, Richard Reid was a threat to the whole aircraft whereas this guy was just violent towards one person and I doubt he constituted an actual threat to life. If one is travelling alone and one tries to intervene the likelihood is that it's just you vs. him...and you might end up getting injured yourself with no benefit to the original victim. The other passengers and the crew might come to you're aid...but what if they don't?
If you can convince other passengers to help you or are travelling with friends who you know you can count on...then I'd go for it!