They have two effects.
1. They change the distribution of a good from a lottery, to a 'whomever pays more gets it' auction.
2. Depending on how they acquire the good, they may or may not have a positive impact on the original vendor.
Because of #1, depending on your personal values, you can make a very compelling argument that lottery-based distribution of scarce goods is fair, and that turning it into an auction-based distribution (While pocketing the difference) is immoral.
#2 is applicable for things like concert tickets (Where scalpers take on risk, and provide guaranteed, but bounded revenue for the artists/venue), but is probably less applicable for video games/devices (Where unsold scalper inventory will likely be returned for a refund - at no risk to the scalper.)