ok first off that slippery slope referred to here is the domino theory - which is a faulty idea of the causality of events - we can say a slippery slope regarding events is likely faulty because unless the causal chain between any two events is very tightly linked our understanding of causality is not sufficient to understand it. That is to say we have a very tight link between a domino falling, hitting another domino and toppling it, but we do not have a very tight link between a country going communist and then another one later. Hence, every causal claim requires a separate argument.
The slippery slopes being discussed here are not about events and the causes that link them, but about the applications of technology and to a certain extent about laws being used beyond their original mandate. This kind of slippery slope is a logical one.
Thus the technology being used for this mean that it can be used for other things - what kinds of things can it be used for? Are there things that people would like to make illegal or that are illegal now that this technology can be used catch people infringing on these hypothetical laws. Thus - if we allow this technology in our devices now are we opening ourselves up for other potential uses for the technology in the future that will hurt us.
If this argument seems the same to you as the domino theory and that we must take every hypothetical problem when it actually occurs I wonder how you are ever able to plan for any eventuality?