Not really. The point your parent is making is that prions themselves don't reproduce like viruses and bacteria. Its basically impossible for a large scale breakout to occur and spread.
From my (ignorant, despite being interested in prions for decades now) perspective, you have something that (1) can replicate, (2) is durable (3) is harmful, and only the relative rarity of prions in general (because 1 and 3 are physically unusual to combine) have kept them from being a general problem. As we tinker with DNA and thus look into creating new proteins and factors that would influence protein-folding, I'd think it's worth taking the matter seriously (though not fear-mongering), certainly as part of our need to understand proteins better anyway.
What are my faulty assumptions?
A virus can overtake a cell and mobilize its resources to create a bajillion copies of that virus. A prion can transform only as much copies of that protein as that cell has made in its normal processes.
A virus requires a cell to replicate, bacteria require a much more limited range of hospitable environments.
Both bacteria and viruses "attempt" to create exact copies, just as a prion does. Admittedly prion replication probably has more accuracy, but that prions occur at all indicates the process allows for natural selection.
These don't seem to put prions outside of the "replication" category - they replicate by encountering other proteins, so they are in a body. Their rate of replication is limited (or boosted) by the rate of encountering these proteins. They attempt to create copies of themselves with the chance of failure or different end result.
They can't reproduce outside of the body, but neither can viruses.
It’s orders of magnitude less reproduction.
One of the characteristic features of prions is their resistance to a number of normal decontaminating procedures. These pathogens are resistant to processes affecting nucleic acids, such as hydrolysis or shearing [9]. However, agents that digest, denature, or modify proteins do have activity against prions [7]. The PrP purified from the brains of scrapie-infected animals (PrPSc) can be inactivated by prolonged autoclaving (at 121ºC and 15 psi for 4.5 hours), or immersion in 1N NaOH (for 30 minutes, repeat three times), or immersion in concentrated (>3 M) solutions of guanidine thiocyanate [10]. However, certain cautions prevail; it appears that inadequate autoclaving can establish heat-resistant subpopulations that fail to diminish with a further cycle of autoclaving [11]. Stainless steel instruments also may retain infectivity even after treatment with 10 percent formaldehyde [12,13].
Newer decontamination techniques are being investigated. There has been some success in sterilization using a combination of sodium dodecyl sulfate (SDS), proteinase K, and pronase [14]. A radio-frequency gas-plasma treatment has been shown to effectively decontaminate surgical instruments [15]. Another group has tested a decontamination formula combining copper metal ions with hydrogen peroxide [16].
>"combining autoclaving (even at 121 degrees C) with a sodium hydroxide treatment is extremely effective." https://www.ncbi.nlm.nih.gov/pubmed/10658760
Usually there is some sodium hydroxide in standard sodium hypochlorite bleach solution as well though, perhaps that explains why they reported it is the most effective of the chlorine bleaches.
As it is, very few proteins in humans have alternate favorable form (by luck or selection?). The exception appears to be the extremely complex and relatively new nervous system of mammals. I'd guess that our immune systems might be another place to look, but that is very highly tested.
Frankly, this seems like a susceptibility that is rare because it is chemically odd not that there is a lack of potential exploitation. Luckily, the range of creatures that share our respiration system far exceeds the range of creatures which share our recently evolved nervous system.
> In a particularly vexing twist, prions are also nearly impervious to destruction, even when attacked using a strenuous combination of disinfectants, heat, and pressure.