How much of an idiot do you actually have to be to not understand the full mess this will cause? Here, I'll explain some things to you:
To begin with, the license you pay for is license to USE, NOT to redistribute, those two are COMPLETELY different.
Second, HOW is it any different than someone buying an album from a licensed distributor and selling it in the open market (something which is actually ILLEGAL in most European countries since you require a redistribution license)?
Third, physical copies deteriorate over time and are, like their name suggests, PHYSICAL, meaning you own the actual thing, licenses for digital products are more akin to video clubs of old where you payed to watch a movie, not sell it after watching it, but instead of having to return the movie afterwards you keep it for infinite uses, you can't treat physical and digital the same under any circumstance, one is actual ownership (but even this prevents redistribution and is highly illegal despite owning it) and the other is simply permission to use something.
Fourth, the "basic consumer rights" are there and have always been there, don't like Steam's terms? Go to GOG or buy physical, simple as that, nobody ever forced you to use Steam, YOU of your own accord accepted their terms and conditions, that's called consumer choice and it's by no means a violation of consumer rights. What you are supporting is violation of copyright ownership though, since, again, unlicensed sales of a product that contains copyright is actually illegal. The reason you can sell physical things is because of a loophole in the old laws that treat those sales as sales of the disk/cartridge rather than the actual data on it.
Fifth, for the last time, allowing the reselling of something gotten for FREE or heavily discounted means that the storefronts straight up LOSE money because actual product sales will plummet and Valve only gets a small part of the earnings from each game, the largest part goes to the DEVELOPERS and that will pretty much quite literally kill any Indies or small developers altogether unless they flock in droves to itch.io (which will also be affected by this BS for the record), so screw Indies and any non-AAA company, right? If this passes the only companies that will be able to afford to develop any more games are the huge budget AAAsholes with pay to play 60€ titles (and that's hoping they don't jack up the prices further to make up for the losses).
Sixth, I'll also bring up once more how this can allow money laundering among other things. Also, the sheer volume of transactions that all this will entail will be more than enough to down servers often at peak times or allow for things to slip past. To add to that, you DO realize that if you sell something you are LEGALLY REQUIRED to include it in your tax report, whether you got money physically or digitally, right? Unfortunately, that also means anyone under 18 will either be unable to resell games or will have to go into their own separate tax report from their parents, on top of Steam having to validate EVERYONE's age (aka you have to give even more personal information out to them and legal documents proving age and even tax papers to cover the transactions as you will essentially be considered a seller), as otherwise they can't legally allow you to resell something on their platform in exchange for actual cash (before you say "hey, they do that with skins/cards/etc.", under the law those are considered as too small transactions to be recorded since they are, for the most part, under 1€ each, but if you look at Steam's explanation on legal things you will see them mention how for larger transactions you need to do all the tax stuff I mentioned).
That should do for now, but that's not even half the reasons, just bored of typing, I assume you can predict the others without lengthy explanations like how this will only affect EU accounts so will cause a lot of troubles with regions, how this law if successfully passed will affect ALL storefronts regardless of those selling licenses or products directly and so on
PS: Just to give you an analogy of your point about "I should be able to sell my license", it's like having a Netflix account which grants you licenses to watch shows basically but you want to be able to sell the license to watch X show to someone despite keeping the account yours, see how absurd that sounds? If you REALLY want to sell your old digital stuff, sell the account altogether, that's legally allowed AND is done in mass scale in many auction sites, simple as that, then with the money you make re-purchase the 5 or so games you want to keep and you still have a ton of money leftover.