I can't imagine Valve won't find some loophole or way around this. Being able to resell digital games would destroy that economy. A possible outcome would be games in France are never on sale and they can only be traded within the French Steam economy. Can Valve still take a cut of all sales on their platform or add fees? Very curious how this turns out, but I feel like it's 50/50 whether this makes things better or…
Game sales over time generally resemble a power distribution. Most sales happen within the first week or so, then sales follow a steep drop-off. There are of course exceptions in the indie game community, but AAA publishes build up to a tidal wave of marketing for release day, then things kind of simmer down.
So a second hand market would cut into the tail-profits. Certainly not desirable for studios, still but quite a few jaunts away destroying the economy.