There are non-fallacious uses of the term. E.g. "The Slippery Slope: How Small Ethical Transgressions Pave the Way for Larger Future Transgressions" gives some experimental examples:
Many recent corporate scandals have been described as resulting from a slippery slope in which a series
of small infractions gradually increased over time (e.g., McLean & Elkind, 2003). However, behavioral
ethics research has rarely considered how unethical behavior unfolds over time. In this study, we draw
on theories of self-regulation to examine whether individuals engage in a slippery slope of increasingly
unethical behavior. First, we extend Bandura’s (1991, 1999) social-cognitive theory by demonstrating
how the mechanism of moral disengagement can reduce ethicality over a series of gradually increasing
indiscretions. Second, we draw from recent research connecting regulatory focus theory and behavioral
ethics (Gino & Margolis, 2011) to demonstrate that inducing a prevention focus moderates this mediated
relationship by reducing one’s propensity to slide down the slippery slope. We find support for the
developed model across 4 multiround studies.
In its introduction section the paper also discusses some anecdotal examples.
Fiction writer Quentin
Rowan described a descent into gradually increasing unethicality
as he plagiarized from other sources over a period of years (Cowan
& Carras, 2012). Rowan began by replacing words in his manuscripts with more sophisticated synonyms from SAT preparation
books. By the time he was caught several years later, he was
publishing articles and books that included dozens of pages copied
directly from other sources. Similarly, several major corporate
scandals have been described as starting small and increasing over
time. For example, according to McLean and Elkind (2003, p.
132), “the Enron scandal grew out of a steady accumulation of
habits and values and actions that began years before and finally
spiraled out of control.” Bernard Madoff’s Ponzi scheme (Kirchner, 2010), rogue trading at UBS (Secker, 2011), and phone
hacking at the News of the World (McGuire, 2012) have been
described in similar terms.
And the paper has 4 experiments proving its point that people are inclined for this kind of ethical slippery slope. Of course such experiments aren't usually going to be famous. What you're asking is a retrofitting of theory to prior events that weren't controlled. Interestingly however, the authors do discuss the Milgram experiment (which is famous) in these "slippery slope" terms
The well-known work of Milgram (1974) also suggests the
possibility of a slippery-slope effect. Across a series of infamous
experiments, Milgram found that average people would administer
a seemingly lethal shock to another human being (a confederate)
when the directive came from a reputable authority figure. Although Milgram’s main conclusion related to obedience to authority, it is notable that in these experiments the voltage of the
administered shock was gradually increased over time. Some have
speculated that a “feature of the situation Milgram created that
most likely contributed to the high rates of obedience was the
incremental nature of the task” (Burger, 2009, p. 3). Our theorizing
suggests that if Milgram had abruptly increased the voltage from a
minor shock to a life-threatening jolt, rather than following a more
gradual trajectory, many more participants would have resisted this
act. However, because Milgram ran only conditions with gradually
increasing shocks and did not consider situations involving abrupt
changes, it remains unclear whether the slippery-slope effect
played a role in the participants’ behavior.
As well as some not-so-famous prior work:
One notable exception to the single-trial format is the work of
Gino and Bazerman (2009). Across four studies, they placed
participants in the role of an auditor who had to either accept or
reject estimates made by a third party regarding the number of
pennies contained in a jar. The auditors were financially incentivized to approve high estimates, even though they were required to
check the estimate periodically. Using a multiround design, Gino
and Bazerman found that people were more accepting of the
unethical behavior of others when unethicality developed gradually rather than abruptly. In an organizational setting, this ethical
erosion might be similar to an accountant performing an audit for
a client who gradually skirts the generally accepted accounting
principles rather than blatantly cooking the books. However, this
research focused exclusively on acceptance of the unethical acts of
others as opposed to one’s own propensity to engage in a slippery
slope of increasing unethicality. In our study, we build on these
findings to ask a different question: whether individuals themselves are prone to a slippery slope of increasingly unethical
As for the study itself it test 4 hypotheses, the latter 3 are basically delving into the details of how first one occurs:
Hypothesis 1: Over a series of ethical decisions, people will be
more likely to engage in unethical behavior during the final
period when potential unethicality develops gradually over
time rather than abruptly.
Hypothesis 2: Over a series of ethical decisions, people will
become more morally disengaged when potential unethicality
develops gradually over time rather than abruptly.
Hypothesis 3: Moral disengagement will increase unethical
behavior during the final period.
Hypothesis 4: Moral disengagement will mediate the relationship between a series of ethical decisions in which potential
unethicality develops gradually over time versus abruptly and
unethical behavior during the final period
Although there are many anecdotes about the
slippery slope in the business world, our results provide the first
empirical evidence that we are aware of regarding susceptibility to
increased unethical behavior over time. Additionally, we found
strong effects using three different tasks and different measures of
unethical behavior: Exposure to slippery-slope conditions more
than doubled the rates of unethical behavior in our studies.
The fact that the Wikipedia article was written by someone with a focus on logical fallacies with non-fallacious usage tacked to the end speaks more to the fact that Wikipedia still has crap articles on some topics.