Our entire legal system is predicated on common law precedent. So it is very valid in many cases to argue that allowing something good now, might set us up for something very bad later.
You think people elect for bad things? Bad governments, bad software or privacy violations? They chose things that are full of rhetoric and promises of good things then those bad things get snuck in off the back off relaxed regulation, or existing software adoption, etc.
Take Facebook as an example, people didn’t sign up to it thinking “I wanted to be tracked around the internet so I can have personalised adverts” nor dis Zuckerburg think “Wouldn’t it be good to create a platform that could latter be used for rigging elections”. No, instead we got there because of a serious of good ideas that slowly got abused.
There is a saying that goes “The path to hell is paved by good intentions.” I’m not a religious man but I think that beautifully illustrates how slippery slopes are not a logical fallacy.
By itself no, but it is often used fallaciously. Such as in this case, when someone is opposing some good thing on the basis that that good thing might, some day, lead to bad things.