All the arguments in favor of this seem to amount to "install some malware and give all your data to the Chinese because maybe in the future it will be better."
This is possibly one of the better arguments that could possibly be made against the entire thing. You can't have a terrible product on your hands and say "it'll totes be super cool you guys, i can see the completed thing in my head already, just wait a few years and give me money while you're here" and actually be taken seriously by anyone with a brain. If there is a gigantic outcry against your product, you have to work twice, even thrice as hard to please people who're telling you just how terrible your product is. If a company doesn't care about consumers' interests and criticisms, then why would they even use their product at all?
An example I know personally is Elder Scrolls: Legends, when back in September 2018 Dire Wolf passed the development to Sparkypants Studios. When the new client was finally released, after months of anticipation, it was a giant mess, everything was clunky, slow and generally bad. Players were angry, but Sparkypants kept the communication going, fixed a boatload of bugs and generally made the game better. They didn't go "dun care lol" and ignore a giant mob with torches and pitchforks standing at their front door. Despite the absolutely horrendous first impression, they redeemed themselves in the eyes of the community by working under the conditions highly unfavourable for them, just to satisfy their customers, and are now quite liked. Amends have been made.
Epic Games, on the other hand, don't care about the people who tell them what aspects of their store can be improved, they will just keep making games exclusive for their platform - practice that consoles have been laughed at for for years - throwing money at them and hoping the problem solves itself. Say what you will about Valve, but they are willing to experiment with Steam, for better or worse, and take feedback from their community and developers. Epic Games will not do that, not in the foreseeable future at the rate we're going, at least.
Also, a question might arise from some: "But Epic Games still makes games, and Valve doesn't, therefore Epic is better". Let's take a look at Epic's latest games. Ever since their success with "Chest-High Wall Simulator" AKA Gears of War, they've been regurgitating this formula for almost a decade. Bulletstorm was essentially Gears of War - a dull, brown chest-high wall fest with fat space marines - but from first person perspective and less serious. Infinity Blade, an iOS exclusive trilogy of games, was
removed in its entirety and is now derelict (you can still download and play them if you bought them, but is there much of a point to that?).
Paragon and
Unreal Tournament reboot were both killed in development to focus all of their teams on Fortnite. And Fortnite... Well, I'm fairly certain Save the World mode is basically dead until it goes F2P (and even then it's not a guarantee), and the Battle Royale will be milked until there's no life left. The game's only positive is the memes, and even then I wouldn't have missed much if the game was never created.
I tried to summarize my thoughts as concise and understandable as I could, but I am severely autistic, so it's nigh impossible. There are other issues that can be tackled, like Epic strong-arming devs from Steam with money and Unreal Engine, but I am not the person to do that. Steam isn't perfect either, of course, there is always room for improvement. A different company could've jacked the prices on games just for the convenience of not leaving your house, but having Steam as a monopoly, with its regional prices, regular sales and just generally good reputation for more than a decade, is not the worst. If there is a good competitor, people will start using it more than Steam. Epic Games Store is not that competitor.
Also, not being Tencent's bitch and not having spyware and malware might've helped not make a bad first impression. But because Tencent owns most of their stock, they'll oblige Epic to have them on their platform no matter what, so in the end this is all meaningless. You decide what you want more - a generally stable monopoly or a competitor that uses dirty tactics and malware.