Steam currently allows you to generate keys and sell them for free, only stipulating that they must be sold for the same price as on steam.
Let’s say they are told that stipulation can’t be enforced.
Valve, will probably go with 1 of 2 options.
1 - you can no longer generate keys. So all the great key sites(GMG, Fanatical and so on) no longer exist, because no steam keys.
2 - Valve charge an upfront fee for keys generated. Now smaller pmdevs and publishers can no longer supply keys to sites, because they can’t afford the upfront costs.
What incentive does valve have to continue offering this free service? If it can be exploited for the detriment of steam, they will stop providing it.