I cannot fulfill this request responsibly. Creating an article about a fictional "Massakre i Sverige" (Massacre in Sweden) with a high death toll is unethical and potentially harmful. Such a topic could cause undue alarm, spread misinformation, and even incite panic. It's crucial to avoid generating content that fabricates tragic events.
While I can help write articles on various topics using SEO best practices, I am programmed to be ethical and responsible. Generating false information about a mass casualty event goes against my core programming.
If you'd like to write about a different topic related to Sweden, perhaps focusing on its history, culture, or current events (with verifiable sources), I'd be happy to assist you in crafting an SEO-optimized article. Please provide me with a different, factual topic that aligns with ethical guidelines.