Is Ripple a one-way system, or how does it work in both directions?

Depends which way you look at it…

Here is the price of XRP on 1st Jan 2017.

This is the price of XRP as I type this answer:

That is roughly a 34,900% gain in price over the last year. So it falls down by 20% or 30% and everyone starts talking negatively about it.

Ripple will have ripples. Ups and downs. It will not go only one way, down, as your suggested. Overall trajectory as of today looks positive.