Law Changes and Slippery Slopes

(Cross-posted from the other place)

Apparently, there was a TV programme in Australia the other day in which a there was a discussion of assisted dying.  It got reported in The Guardian, largely on the basis that an 81-year-old audience member kept calling Margaret Somerville "darling" and then got mildly sweary.  I've only seen those clips from the programme that are linked in the Graun's report, so I'm not going to comment on the tone of the debate in particular.  Rather, I'm interested in one of the responses to the programme, from Xavier Symons, writing in The Conversation.

Symons takes the opportunity to unpick the idea of a slippery slope argument - in this case, the claim that allowing some forms of assisted dying will commit us to allowing... well, that's open-ended, but it's sufficient to say that it'd be terrible.  We'd want to avoid terrible things; therefore, the argument goes, we shouldn't allow any of it.  This is well-worn stuff in the seminar room, but it's a mode of argument that refuses to die.  Quite correctly, Symons points out that

there is a need for empirical evidence or sound inferential reasoning to support the claim that event B will necessarily (or probably) follow on from event A.  Without this evidence, the argument is invalid. I can’t just claim, for example, that the legalisation of medicinal marijuana leads to the legalisation of ice - I need to show some empirical or logical connection between the two.

So far, so standard.  (I'd say "unsound" rather than "invalid", because the validity of an argument doesn't depend on its evidence - or, at least, not in the same way; but that's a small matter.)  He then makes another move, which is a bit more interesting:

But (and it’s a big but) there is such a thing as a good and valid slippery slope argument.  A good slippery slope argument demonstrates a causal or probable relationship between event A and B, such that event B can legitimately be expected to occur if event A is allowed to occur. [...] There are, nevertheless, compelling empirical and logical slippery slope arguments available to defend more modest claims about the “normalisation” of assisted dying.

Is this correct?