They are either:
a) platform - so all legal stuff is perfectly fine, they have to stay neutral, then they can not discriminate against any dissenting views, but are not liable for any crazy user
b) publisher - no one could call it "censorship" as they have full discretion in selecting the stuff to publish, it would be even natural for them to develop some political bias. However, they should be picky and remove potentially dangerous content as they are liable for it.
OK, so what are they? They say being a platform which grants them legal protection of not being sued for posted content, while also heavily use right to ban people and videos which they dislike for ideological reason.
While the rumours had been circulating for a while, right now leaked documents show that they have quite strong distaste toward right-wingers and and try to skew the system against them. (Promising to prevent "Trump situation" in 2020) Nothing wrong about it per se, as long as you are publisher and exercise your editorial discretion. (if you are a neutral platform, such behaviour more resembles utility company cutting off electricity for political opponents)
What right wingers are trying achieve is end their ability to have the best of both worlds, and force them to choose whether they are actually platform or publisher. Apparently under contemporary regulations they managed to stay in this beautiful grey zone. Technically they would not be forced to accept dissenting views. However, if they are publisher, that would destroy their business model, as they would have to check every video to avoid some random people defaming each and later deciding to sue instead a rich company that was the publisher.
EDIT: Concerning cpast comment, it's becomes a bit more tricky when look at the bigger picture:
§ 230 (c) Protection for “Good Samaritan” blocking and screening of offensive material
(1) Treatment of publisher or speaker
No provider or user of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider.
(2) Civil liability
No provider or user of an interactive computer service shall be held liable on account of—
(A) any action voluntarily taken in good faith to restrict access to or availability of material that the provider or user considers to be obscene, lewd, lascivious, filthy, excessively violent, harassing, or otherwise objectionable, whether or not such material is constitutionally protected;
The ratio legis was to protect a "good Samaritan" that removed most "filthy" content, not give a blanket endorsement for any kind of editorial process (censorship?). Had that been this intention the whole following point would be pointless.