You can definitely ignore theme in your writing, since your writing is your creation to do with as you please. That's the beauty of the arts! 💜 You get to express yourself with or without consideration for theme, rules, genre restrictions, or anything else society demands. While scholars and marketing gurus do have the expertise to tell us what sells, history is filled with artistic pioneers who stayed true to themselves without consideration for the rules, and some blazed new trails leading to the establishment of rule exceptions and even whole new rulebooks.

And I understand and agree with your point about keeping the work fun and not overwhelming it with theme. Balance between expression (which satisfies the author) and entertainment (which satisfies the reader) is how we ensure that our expression has an audience, and as you point out, too much focus on academics can make your work less entertaining. That's why we spend only one day on theme, one day on marketing (including identification of target market and genres), seven days on character, and twelve days on plot.

But your theme is there anyway, without your knowledge or consent, whether you identify it or not, and if your story sells, it's probably thematically consistent. 😉