First of all – let’s be decent human beings
In general the only argument that should matter is that some of our users have accessibility needs and you should build your web content in such a way that it is accessible. Brad Frost’s excellent (though controversial) article says much more than I ever could about this issue.
Accessibility is not just for disabled people
It’s easy to ignore disabled people if you don’t know any personally. But there are plenty of things we might be able to empathise with to help you understand.
As part of my job I spend a lot of time on computers and then some of my hobbies involve me staring at a screen too. By the end of the day my eyes get tired so I actually view all websites zoomed in at 120%-150% zoom. Websites with poor accessibility are harder for me to use and as a result I find myself less engaged.
A good friend of mine suffers from severe RSI and is much more likely to navigate your website (or app) with a keyboard than with a mouse – if he can. Here are some things you can do to make it harder for him to use your website or app: don’t treat keyboard focus the same way as mouse hover or remove outlines from focus elements so you know where you are tabbed to.
My little cousin has Autism and is an avid consumer of technology. I would hate to think that someone is willing to make a website visually difficult to use for people with cognitive difficulties. Keeping your links and buttons consistent, having a visual hierarchy and an ordered structure to your content are vital for people who have difficulty with cognitive tasks. This is not just for people with autism or similar conditions but also for users who are not web-savvy too.
The selfish reasons
OK let’s suppose you have no care for the blind, handicapped or the disabled. Let’s say that you also don’t give a damn about my poor eyesight or my friend with RSI. There are some selfish reasons that accessibility matters too.
If you structure your website in such a way that people with assistive technologies can use your site then it will have better SEO. Why? Google uses a bot to crawl your website much like a screen reader. If you structure your markup in such a way that is easy for a screen reader to pick up then you structure it in a friendly way for search engine crawlers too.
We are not that far away from brain interface devices (at least simplistic ones that work on an EEG) and we have some already available today. Not only that but we already have voice interface devices like Google Glass and Siri. These technologies are not going to interface with your website the way a human would. Making your code accessible friendly makes it more future proof for these technologies. And that is just what we know about – we have no idea what technology is to come. Plan for the future by being accessible now.