Valid criticisim is one thing. But valid criticisim requires actual deliberation. It requires thought, logic, and supporting evidence. It can't just be a matter of opinion.
Being enthusiastic about a launch is natural. There's a certain amount of hype and excitement that always goes into such an event. It's easy to get wrapped up in this excitement, and perhaps set aside some of the informed critique that you might otherwise engage in. A little well-meaning criticism can actually be helpful in such a situation, bringing some much-needed realism to the participants. Proper criticism can help to temper expectations, and prevent people from getting too wrapped up in the hype.
I try to keep my critique of the situation in this vein. People ought to be a bit more realistic about what they expect from a launch. Launches are the worst time to purchase any video game platform. By necessity the game selection is the smallest that it will ever be at launch. Even a console with a stellar launch-lineup will still have fewer games at launch than at any other time. The potential for hardware issues is also highest at launch. We certainly saw that with the Xbox 360. (just one example, if one of the more notorious) The rumors of left Joycon syncing issues hints at such hiccups. Hopefully this is something that can be sorted out through software, but it is typical of launch hardware difficulties. And long-term viability is rarely determined at launch, so you're always gambling on the future of the system. It may get big and have great support. Or it may tank and have very little support, you don't know. None of us know. I've been quite good at predicting such trends and even I don't know.
All that said, I'm not cancelling my pre-order. This is partially due to Nintendo's long-term track record. When it comes to hardware, they've always been great. They just make sturdy systems with low failure rates, it's always been one of their hallmarks. And their track record on software speaks for itself. They're still in this market because they are responsible for some of the greatest games of all time. And their games are on their hardware platforms. As much as some consumers lament this fact, I'm fine with it.