Well, he should have been feared since he was the dirtiest player I have ever seen... maybe in any sport. He would get thrown out of the league in just one game if he were to play the way he did with today's concerns over health and safety of players. That's what cracks me up about the NFL's romanticizing about Butkus... guy would rip people's helmets off at the bottom of piles just because he felt like it.
Don't get me wrong, he was a great player, but there is a double standard when it comes to Butkus and how we'd react if someone did 1/100th of the things he did in today's league. There would be outrage, guy would be called a thug, etc.
Also, his teams were always really, really bad, which doesn't help his standing in an all-time sense.