Separate Feeding Container v. Feeding in Enclosure?

[phenyx]

What's the general consensus on feeding in the enclosure versus feeding in a separate dedicated container?

I went across the Bay today to a reptile store in Pinellas. One of the guys there was incredibly knowledgeable and answered today's list of burning newbie questions, but there at the end he was vehement that I should never feed my snakes (a baby BRB and a baby normal BP) in their enclosures because they will eventually start attacking my hands every time I put them in. I tried to tell him I reach into the enclosures far more often for non-feeding purposes than for feeding but he was adamant. He even sent me home with a handful of paper bags and told me to use them for feeding until I can set up a dedicated feeding enclosure because apparently anything else is BAD SNAKE OWNER. He was a little over-the-top.

So is this cage aggression, chomp-the-hand scenario an actual thing? I remember reading in some post somewhere on some forum or another that it's a myth, but honestly I've done so much reading lately it's all blurring together.