Learn English – What does “tea juice” mean in this context

It is indeed a rhetorical use of 'catch up with': a deliberately uncommon use, which attracts readers' attention so they will read the explanation.

The author contrasts the attitude he attributes to older people—that they are slaves to “long term plans that basically take a big chunk of your soul over a long period of servitude”—with the attitude of his own generation—“Life nowadays is INDEED about the NOW!“

His “catch up” figure thus represents the long-term plans of his elders as an unceasing effort to get ‘in front of’ who they are, while people of his own generation abandon that pursuit and turn back (so ‘back is the new front’) in order to ‘catch up with’ who they are.

The argument to a 'slippery slope' lies precisely in the inevitability which is claimed for the final undesirable outcome. Once you step onto such a slope its slipperiness is so great that you cannot achieve the traction or friction which would be needed to stop at some point along the way: you must continue all the way to the bottom.

In 176, "All these things could happen, but it is hard to prove that they will happen" is an argument against the slippery slope: the end is not inevitable, the slope is not so slippery that we cannot stop at some point short of the bottom.

In 177, "decision two" represents the bottom of the slope and "decision one" its top. Even though it "was not thought to follow from decision one when decision one was made", it did in fact "follow from it after all". Once decision one was made, decision two followed inevitably: that is "a true slippery slope".