Given that anyone could set up their own instance with whatever rules they like, I don’t think it would make sense to say that “Lemmy” is “liberal”. It’s kind of like asking if email is liberal.
However, it is certainly the case that different instances have different political leanings as established by the instance administrators.
Likewise, communities are governed by their moderators, but as this is Lemmy, if you don’t like the way the moderators run their community, you can create a community of your own. Then you can have an echo chamber filled with everyone who agrees with you!
So, it is what we make of it. We can have liberal, center, or conservative echo chambers if that’s what we want, or we can have knock down drag out fights with people who will never agree with us.
It’s important to remember that in Lemmy downvotes are like the points in Whose Line Is it Anyway: they don’t matter.