AIDS is directly spread through a knowing contact. You don't just "Accidentally AIDS". You might not know you have it; in all other ways, it is directly comparable to an accidental gunshot. Likewise, cancer has a myriad of causes, most of which are completely unintentionally instigated by the sufferers. Similarly, no one hops into a car and says "I'm going to kill a whole bunch of people." Yet it happens.
The primary association between the aforementioned causes, and the comparison to gun violence, is simple. People die. Cars crush, AIDS decays, cancer devours, bullets make holes. To be blunt, death is a part of life. Why pick any one "cause" over any other? (And to answer your question, yes, you can legislate limits on diseases, but it infringes on morality and rights: AIDS victims -cannot by law- have sex, for example. Repeat for any STD.)
And don't worry about being skillful at writing, friend. I have a rather uncommon ability when it comes to writing, and I do not expect the same of anyone. You are perfectly understandable. 
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