I really don't know. I do think people abusing the system isn't a huge problem so it's not something that needs to be worried about too much, I don't think you can just roll up and demand a test, your school will identify you based on how you work in class and I doubt many people would want to cheat in that way. Most school age students would just want to be normal. It is hard to accept because I think most people would do better in exams if they had an extra half hour!
Generally I don't know how I feel about it. I had access arrangements in my exams (rest breaks and separate room) and I wouldn't have been able to achieve what I did without them without them, I think I would probably have failed most of my exams so I certainly understand why access arrangements exist. However, I think my difficulties (in theory) were things which would hopefully not be an issue by the time I reached the workplace whereas if you take 50% as long as everyone else to do a task, or can't read anything for yourself you simply aren't as good a worker and maybe exams should reflect that. Emphasis on the maybe, I don't know the extent of allowances which need to be made in the workplace and I do still feel uncomfortable with the idea that you fail a maths test because you couldn't read the question or something when your maths knowledge is solid...