Yes it's being going up overall (a lot), but even if you just look at a chart of the last 12 months, it hasn't dipped more now than it did a few times last year - I can see why some people think it's going to keep going up for a long time, and others the opposite, but I can't see why anyone would think "great it's always going up" until now and be scared by a relatively minor dip down here.

"past performance... future returns"

The S&P keeps going up because if it went down the fed would lower interest rates until it started going up again.