All altcoins can become a scam at any time, even those with strong infrastructure, utility, a powerful community, a large fund and a real product. Even ETH can turn into a scam under certain circumstances.
ETH is turning centralized, so yes, there's a high probability it will become a scam in the future. I'd say there's no altcoin you can trust these days due to their extremely-unpredictable nature. If there's only one coin I'd trust, that would be Bitcoin. It's the original cryptocurrency that started it all with a proven track record of development and innovation. With decentralization at its focus, I believe BTC will last for generations.
If you're still considering getting into altcoins, I'd suggest you diversify your investment as much as possible. This will allow you to minimize risks of loss if something unexpected happens in the long run. I usually aim for coins with active development and innovation and some old ones with an established presence in the crypto/Blockchain space (eg: Litecoin, Dogecoin). Play your cards right, and who knows? Maybe you'll get lucky and strike it rich in the future. As long as you don't investment more than what you can't afford to lose, there should be nothing to worry about. Just my opinion
You glorify Bitcoin - and yes, its decentralized and has paved the way. But let's not forget that Bitcoin too has its flaws, primarily in scalability and energy consumption. And while Bitcoin has a storied history, dont get too trapped in nostalgia.
About altcoins: lumping them all as "extremely unpredictable" is a lazy perspective. Like any investment market, there are gems and duds. It's about doing rigorous research. And really? Dogecoin? A meme coin with unlimited supply and minimal development as your "established" example?