Better to be a happy MA, than an unhappy PhD. Most people on the spectrum seem to not do well in higher paced environments. Based on what you've said, this fits you, so you would most likely be unhappy in the high paced academic environment. Picking a career isn't supposed to be about picking the highest level you might be able to achieve, or the highest salary. It's supposed to be about finding a job that is a good fit for your abilities, and that also is one you will like doing.
As for disappointing others, it's your life, and you are the one who has to live it. Besides, they aren't going to be disappointed in you finding the work type and level you will most like doing. Just tell anyone who questions your decision, that you don't want to work in such a high paced and stressful environment, as you would experience in the academic world. The world would be a better place if more people sought out less stressful work.
Remember, such decisions are not engraved in stone. If you try something and don't care for it, you can always try something else.
What ever you decide, good luck!
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau