Is having a disc brake on a single speed bicycle a bad idea? I talked to a bike shop that sells a lot of fixed/single speed bikes. I asked them if they could sell me a single speed with a disc brake on the front. The guys said no because:


It will be hard to find a frame that supports that
It is silly and not really needed and a waste of my money


If he is correct about the money part, then what would be a better place to put that money?

I bit of background: I commute year round, and I really like the stopping power i get on my mountain bike (with disc) during the winter / rain. I also tend to ride 20-25mph in Boston.
Well, there are lot's and lot's of commuter bikes with internal hubs and disk brakes. I see 
no reason why a single speed wouldn't work as well. 

A google search for "single speed cx bike disk brakes" turns up this beauty. 

http://allcitycycles.com/bikes/nature_boy_disc

There are low budget models out there as well. Nashbar 29'r Single Speed

Swobo makes one, you can build a Surly Straggler up as a single speed. 

Getting exactly what you want will likely cost a bit more, but that should be
for you to decide if it is worth it. If you're going to commute in the rain,
my opinion is that a disk brake is well worth the extra expense. 

I'd go to a different bike shop.