Do you think Jesus became popular because people said, "Jesus is a good guy, but don't believe everything you hear about Jesus." NO! People said, "Jesus can walk on water! You will go to heaven!" Look at where Christianity is now.
If only people at the time were rational and would keep it to "this guy is great talker, but it's not like he can do supernatural things, obviously".
On-topic:
I think Gavin and Erik have a right to their opinion just as you and I have. They are often asked by the press if it would be a good idea to invest in Bitcoin and saying that it's unwise to put all your eggs in one basket is excellent advice, under any circumstance.
In fact, although I am quite certain Bitcoin will survive and will go to $1M per coin, I keep telling friends and family never to invest more than they are prepared to lose. They can always decide to follow their own judgment.