You’re offering in you blog the option to subscribe to your newsletter. If the checkboxes are options regarding the contents one prefer, they’re like options while purchasing a product and so they’re not different personal data processing options. So, yes, they can stay prechecked.
If a checkbox regards the possibility to share the personal data with a third party, that is a different use of data and it cannot be prechecked (just an example).
Be clear in your form what you’re going to do with data and if you’re not bundling really different things (like a newsletter, an ebook and the consent to share the data with others) you don’t need to have specific opt-in checkboxes.
You’ll note a change in the offering from now on. For example who were asking for data to send and ebook and then filled your mailbox with marketing message, now ask for separate consent to send those message.
Shortly they could change the form saying: subscribe our newsletter and you’ll get a free ebook. That make clear you’re subscribing a newsletter and not giving your data only to get an ebook. That is not a trick, is a way to be clear.
Just my opinion.