Like Sega, I don't mind the design. Perhaps the black at the top and bottom is a bit strong, so maybe make it something gentler, like a soft blue or something.
One thing I'd suggest is making the point of the site/organization a bit clearer. I had to read quite a bit to get an idea of what it means to be a member, but I'm still vague. Unless I can get a crystal clear idea of what a site is for pretty quickly, I tend to leave. It needs to be made really clear what benefit there is from being a member, what's expected of me, etc. etc. At the moment, the message seems a bit undefined and wishywashy to me.
I'm not sure I like the color scheme. I don't really care for the black background at all, I think the text would be more readable if it were against a white background with bigger black text. You can choose a few other colors for contrast, but I'm not sure the black and pink is very effective at conveying your message, which could be stronger. I think the text could be larger in general also.
Looking at your site I agree with a poster above, the purpose of your charity is very vague. There is a lot to read before I got an idea of what you are all about...And still am not clear. You need to grab my intrest with just a sentance or 2, get me on your side quickly! Like "cure Cancer"
The main page and every page needs a call to action, this is one distinct activity you want the user to do, I was not sure what this was on your homepage... find out more was the closest, But by nature people will search for more info if you have followed above and grabbed their attention.
I would use "sign up for our newsletter" or donate etc there is not something to make me get involved.
What is it that you want people to do? What is your call to action?
You need a call to action button like: "Start an Ethical Career Now" or "Become an Effective Altruist Now" "Make a Donation Now".
You need to tell your visitors exactly what you want them to do, and take them simple step by simple step toward converting them. Otherwise they will say, cool site, leave, and forget about your site 5 seconds later.
What is your website's intent? To inform? To get a donation? To get their email address?
Figure that out first.