Good choice. Just to elaborate: double opt-in is expected behavior from customer-centric companies, and expected behavior from good actors in the email ecosystem. It's not necessarily required by law in the US, but it's a good practice nonetheless: always make sure you have permission from a recipient to send an email.

Anyone can pass anyone else's email address as input to a form, so simply receiving an address as input is not actually permission. If a newsletter does not employ double opt-in, then it will eventually end up on a list of "single opt-in newsletters" which are used to harass people by subscribing their email to a ton (100s or 1000s) of newsletters that they don't want. People who are the victim of this will rightly mark those messages as spam, causing your email reputation to drop. Random Internet bots will also submit subscriptions using your form with weird addresses for who-knows-what reasons. It's a very good idea to have some data validation to make sure garbage doesn't end up in your list, and double opt-in is one of the best ways to achieve that.

Furthermore, competitors might maliciously attack you by subscribing random email addresses to your list. They can get these addresses from data dumps from compromises (like what haveibeenpwned is using). Sending to these addresses will harm your reputation because recipients will mark as spam, or will fail to interact with your messages which is also a spam signal. Smart malicious competitors will cause you to start sending to spamtraps.

The best defense against being manipulated in these ways is double opt-in. Lastly, your email list as such has more value overall if you know that every single entry was confirmed by double opt-in.

As a corollary, you should remove addresses from the list if messages to the address start bouncing, or if you receive a spam complaint from them; sometimes people are lazy and will mark spam instead of unsubscribing. Ideally, support the List-Unsubscribe feature so that people can unsubscribe from it directly in their email client. A good email platform will help with all of these things.

I consider single-opt-in use of email addresses to be a dark pattern or anti-pattern in most contexts, especially non-transactional contexts like newsletters. Any sort of recurring communication needs double opt-in.