Explain this passage

[Carol]

No: HPFGUIDX 180691

potioncat wrote:
> > I have to wonder again, if the Hat had offered Gryffindor to
Severus, if he would have taken it? Would Lily being there be enough,
or would James being there have been too much?
> 
> Elihu:
> I think that Snape's and James's  mutual disliking was something
which developed over time. Just like Harry and Ron ended up liking
Hermione, Snape could have ended up liking James. In stead, Snape
spent his time making friends with the wrong kind of people, and while
it took Lily nearly 5 years to end her love for Snape, James found it
very easy to dislike him. If Snape had been sorted into Gryffindor, he
probably would have made friends with the same kids as Lily, and his
relationship with James would have probably ended up better.
>
Carol responds:

The only way that would have been possible would have been if Severus
and James had not met on the train and James had not immediately
stigmatized Severus for wanting to be in Slytherin, the House that
Severus associated with brains. By the time that short scene is over,
James has tried to trip Severus, and either he or Sirius (Sirius, I
think, but there's no attribution) has labeled Severus as "Snivellus"
based solely on his name. Any chance for friendship or any willingness
to be Sorted into Gryffindor to be with Lily was, IMO, destroyed by
that encounter. If they'd never met, Severus might have chosen
Gryffindor against his inclinations or been convinced by the Hat to
try Ravenclaw, the House for brains. But James disliked him from the
moment he announced his desire to be in Slytherin, and that was that.

Carol, thinking that Dumbledore is right about Sorting too soon and
thinking that first- and second-years should have the chance to know
everyone in their year and meet with older students from all the
Houses before they're Sorted