Question about Pure Bloods and House of Slytherin

[Carol]

Potioncat wrote:
> <snip>
> 
> Neville's description of his self as "almost all Muggle" makes me 
wonder if JKR just hadn't decided on Squib at that point, or if Alice
was Mugggle-born.
>
Carol:
I don't want to chime in yet on the Squib question except to say that,
IMO, a nonmagical parent, whether Squib or Muggle, would result in an
"impure" bloodline for his own descendants but not for the rest of the
family (say, his nieces and nephews). Fear of Squib children would
certainly cause pure-blood supremacists like the Malfoys to avoid
marrying a Squib, in any case.

But I do want to mention that Alice Longbottom can't be a Muggle-born
or Neville would be a Half-Blood like Harry, who has a Pure-blood
father but a Muggle-born mother and is every bit as much a Half-Blood
in the Malfoys' view as Snape, whose father was a Muggle.

Remember, Dumbledore says in OoP that Voldemort, in interpreting the
Prophecy, chose the Half-Blood, Harry, over the Pure-Blood, Neville,
as posing the greater threat to himself?

Carol, who wants to talk to Potioncat about Snape's death but knows
it's not appropriate for this thread