Why would they be “weaker”? I don’t get what you’re trying to say.
But lots of men definitely do think women are likely to be weaker in computer science. I don't know why they think that - you'd have to ask them?
Yes I can. It's completely reasonable to be observe something even if you can't offer an explanation.
I don't know why some people are racist but I can see that they are.
I don't know why some people are sexist but I can see that they are.
I don't know why some people think women are inherently weaker at computer science, but I can see that they do think that by what they say and do.
If you're presenting that they don't, where is that information coming from?
I don't know how to break this to you... but a lot of people in this world unfortunately discriminate against people based on gender, either consciously or unconsciously.
> where is that information coming from
To give you a concrete example, I was at a conference just recently where the speaker took questions from the audience and when a man asked a question the answer was highly technical, and when a woman asked a similar question the answer was patronising and non-technical as if he thought the woman wouldn't understand like the men did. It was really obvious, and there was no other variable. I see this kind of thing all the time.
I don't know what more to tell you - if you can't see any evidence of men making assumptions that a women isn't going to be as competent in computer science just based on her gender then I think you must be blind to what is happening around you.