People should apply to YC because they believe it would them them build a successful startup, not because they want prestige. If expanding YC leads to a decrease in prestige (alongside an increase in real value to startups, as Jared explained above), that's a win for everybody: more business-builders get access to YC, YC gets to fund more successful companies, and status-seekers can find something else that will look better on their resume.
In this sense YC is very different from the elite colleges whose brand depends on their exclusiveness. The upper bound on YC's expansion is how much startup opportunity exists in the world.
That being said, it’s not clear to me that YC is lowering it’s acceptance rate. By accepting companies from all around the world, it’s pool of potential applications exponentially increases. If YC accepts 100 more companies from 10,000 more applicants that still feels like a pretty exclusive acceptance rate.
What could be going on is that people are comparing the batch sizes now to the batch sizes in the past and assuming the same rate of company applications. I’m not sure if YC publishes their application data, but without it I think it’s tough to say based on batch size alone whether or not YC is statistically becoming easier to get into.
For founders, the reality is that the scaling of YC, fairly or not, does change the perception of being admitted into YC, in that having a larger class size gives off the impression (whether true or not), that the program is no longer as highly-selective/elite. For what it’s worth, I don’t think YC is at that stage and I don’t think the expansion dilutes the YC name (this isn’t like TEDx). There is a big gulf between admitting everyone and expanding class size the way they have been expanded now. Still, as I said, an increased class size can absolutely change the perception, amongst applicants, alumni, or outsiders, that the program is no longer as “elite.”
This isn’t unique to YC. Elite colleges and universities are often artificially limited in their admission figures (Harvard College has about 6600 undergrads whereas Harvard University has like 14,000 graduate students across the different schools and programs) and while some have attempted scale through either extension schools or online programs, there is a not insignificant social construct surrounding the idea of keeping something deemed “elite,” selective.
So everything you write is true. But it’s also true that the perception of scaling can be negative in some ways, even if the program isn’t actually diluted.