I have not weighed in on the book burning issue, but I will weigh in here. Here in the united states, where we have a clear and unimpeachable right to freedom of speech (minus of course inciting speech like yelling fire in a crowded theater, etc.), yes this would be viewed as offensive by some of the population, but still allowed. Given the context of this being governed in the laws of the EU then the EU standard would apply. I am not sure if this is in keeping with the EU laws, it sure feels like it is, but if it is then if they want to continue having access to the EU on Twitter/X then they probably need to comply, as the laws of the United States do not govern other nations. Seems fairly clear to me.
Now, do I agree with it? Not sure actually. I think they should be able to post and send what they want to, within the law, but I think there is also a moral responsibility beyond the legal terms defined in "the law" that operators of sites like this should be expected to uphold. I think the same for Facebook, et al. that they should all be willing to reduce the inflammatory content and reduced the targeting of children and young people in their addiction-generating algorithms, for example. But they have shown only a propensity to chase the almighty dollar regardless of who it harms or how much general harm it does in society. I think that is "more wrong" than what is being sought here in this letter.
Do I feel this is akin to book burning? No, not really. I mean I think an argument could be made, but to me this is not the same thing.
