Adult stepson

I have an adult stepson who is staying with us.

He used to study but dropped out of college and so my husband found him an internship at his work and he seems to be doing well and is considering picking up again his studies.

Here's where it gets tricky. He believes he is of above average intelligence (he actually says that) and he constantly wants to start philosophical conversations with me. I try to avoid them or say that this (whatever he talks about) is not my field. If I do get into a discussion he gets offended that I don't agree, twists or misunderstands what I say, etc.

I think he is smart, he has potential but he misses a lot of the basics. He doesn't even know how to do proper academic/scientific research and never finishes anything he reads, so obviously the idea he has of what an author has said or written is wrong because he has not actually read it, but bits and pieces of it. I tried to explain to him what this or that author he mentions says, and he gets upset, says I am condescending, treat him bad. I have told him I prefer we stay away from this type of topics. It's not that important. I feel like he wants to have this type of discussions to see how I will react. But I really don't want to. Anything I say which is not agreeing with what he says he gets upset. Why create problems out of nowhere? He says we change the world when we make the others see our point of view. I don't mind if he never sees my point of view.

Why is he doing this? How can I avoid engaging in this? I don't want him to feel I do not validate him. But how can I agree when he says things like gender is only binary? And that he has thought of it philosophically and it is so. And if it is not so, I should tell him what is a woman. Like even his train of thought makes no sense. I simply don't want to engage. At the same time I feel I have a responsibility to help him in life, and be kind with him, but I don't like the bad atmosphere this type of discussions create. We don't need this.

P. S. He says don't use don't, not, no with feelings (like when I say I don't want us to have this type of conversations); he says that in psychology it means you want to do what you say no to. What? Trust me, he says, I studied 4 years psychology and philosophy. Every time he says that I want to say: but you only have enough credits to justify 2 years..

Edit to add: He is 22. The existence of opinions was our last discussion. I was talking to his father actually and I said, "that is my opinion"; his father had asked me for my opinion on our kid's school; we are considering whether to change school or not. And my stepson wanted to start a conversation on opinions; that they do not exist. But only objective and subjective knowledge according to epistemology. But he wanted me to agree, actually say out loud that opinions don't exist. Well I don't share that position (really I don't share his opinion on this, but since this is a forbidden word for him, I used the word position). This was not enough for the conversation to stop. He wanted to go on and on, it became a monologue. It was exhausting!