I say go for it. These days, I often avoid trilogies. They so often bore me, because most writers simply aren't up to the task of keeping a setting and characters fresh for that long. Or they have one book they spread with filler, info dumps, and other rubbish to make three - which are released separately and painfully slowly at times. I want to slap them until they get on with it. Basically, most trilogies should not be.
Personally, I use an approach like Niven, or Heinlein or several others have done with many many books. I have a consistent universe, but standalone books. Its a whole damn universe, not like a fantasy world. So I am not bound to one world, or one culture or society. For example, my last book was set on a world that was in fact a long lost colony. It was not a part of the social and political environs of the other novels, but it was still part of the universe. My third novel was an isolated new colony, fighting to survive. It is also standalone. Some of the universe stuff comes into it, but it stands on its own legs. That one is getting a sequel, but in my time, and in no way essential to the first books closure.
This approach has been a lot of fun. I have had the occasional character show up in multiple stories, but they don't have to. This freed me to avoid that horrible 'typecasting' that a series can dump on a writer. It freed me to pursue an ambition of writing several completely different books, to prove that I can, and yet have them able to tie into each other in a consistent way.
A standalone book is satisfying to read in ways no trilogy can provide. Further, the one universe standalone books approach is great for creating what Niven calls "playgrounds for the mind" - where a reader can remain in the universe for a time, thinking about all those what ifs.
Wanting to write stand alone books? Do it! Tell all the marketing majors to get lost, your a writer, they aren't. Just because the marketing boffins see dollar signs, doesn't mean it is the write way to do your thing.