Look at it this way. When you resign from a job with a formal letter, it is considered a legal document terminating your employment of your own volition. It may impact your ability to collect unemployment insurance benefits (it does where I live). But the employer is not allowed to say negative things about you, your performance, etc. as an employee, because it would leave them open to charges of slander if you found out about it.
When you write a letter to Disassociate™ from the JWs, it is considered a legal document, terminating your association with the JWs of your own volition. What happens after that is (a) an announcement from the Platform™ stating that you are No Longer One of Jehovah's Witnesses™, and (b) every JW you have ever known will be required to shun you. The announcement itself is a form of slander, because while no reason for your segregation is given, every JW assumes that it is for some kind of wrongdoing, such as fornication, adultery or even apostasy. Nobody there will ever know if you have an ethical issue with the policies of the WTS or if you disagree with an interpretation of the Bible, that perhaps others have too. It's just assumed that you are an Unrepentant Sinner™.
The WT rule to write a letter of Disassociation™ is like an unloaded firearm pointed at your head. An unloaded gun is a threat without substance. The letter itself is the ammunition they will use to destroy you. The letter is key, and it's up to you whether you want to give them the ammunition. Personally, I wouldn't - and haven't for over 20 years. I still have a relationship with JW relatives. Other JWs... I couldn't care less whether or not they talk to me, they were fair weather friends at best.
PS: In case you are ever approached by two Elders™ and are asked whether you consider yourself to be One of Jehovah's Witnesses™, tell them that your relationship with Jehovah is just fine. Do not answer their question. You don't owe them an answer... they do not have authority over you, except in their own opinion. It's a loaded question: If you say Yes, they can Invite™ you to a Judicial Committee; If you say No, it's as good as a DA letter and they will make an announcement at the next Meeting™.