All parents of special needs children must mourn the loss of the child they thought they were going to get in order to appreciate the child they did get. For some, the mourning period is short but for others is a process.
Jim Siclair, an autistic man said the following:
There are many sad, depressing and even angry moments that you go through as a parent in day to day life while dealing with your child who has autism. In my case as the parent of a child with Autism its trying to get through the constant talking, involuntary body movements, the lack of interest in what you are saying, the emotional roller coaster, the inability to live 'normally' because your time is heavily constricted and so forth. The sadder part is all those around you who think they understand and have it figured out what you 'should' and 'shouldn't' do to make it all better. Autism is life long and that is the frightening part - what will happen when you're not there to buffer the effects of real life for them as people will not understand their awkwardness.
The fact that Jim brought this up shows it is a common issue. It may not be anger towards the child exactly but anger about the circumstances the parent is in that does not change. Keep in mind that anger, sadness and depression go hand in hand and it is very easy to fall into daily doses of that when you see no progress and you wonder "why" or "why me".
The main problem with Autism though is somethings do not change, BUT because of that they must not necessarily be accepted just because we have a knowledge that they do not change - for me why certain things are done the way they are done by one with Autism must be understood by you as the parent but we should not feel that hope of a change or progress being made even if so minuscule cannot be made. However we must keep in mind for the sake of the Autistic child they MUST be made to understand if at all possible through constant repetition / signs, and so forth that whatever action they are carrying out that can affect others will not be tolerated by someone outside of their protected circle. I think it is in this moment that parenting is most difficult. It is not the concern for the child now, but the child who has now turned into an adult and will be responsible in some part of his actions. It is the child who must fend for his part when you are dead and long gone. In society the action of someone if bad enough will warrant you being 'put away' regardless to your mental competency / challenges. This is what is usually thought to us as children - how to be good citizens - just because someone is Autistic does not mean they are excluded from what society expects of them - be law abiding and so forth. Hence we must ensure every possible way that the Child with Autism recognizes that certain actions have consequences - for their sake.
For instance there is a person I know with Autism who has a fetish if you will and will attempt to hold or be around women inappropriately. I will not go into detail about that, I do not think it is necessary for the illustration I am giving. He has been told many times how wrong this approach to women is but it as though you never told him. The only thing that may bar him is if you show anger about what he is attempting to do and even then he may be puzzled about why you are angry. Now, my point here is not that showing anger changes anything for the person with Autism, but it does temporarily put a stop to something, usually an undesired action that if left unchecked or handled in a 'normal' way will have worst consequences for those around the Autistic person. You do not want to be angry or sad or whatever but such is brought out of you when you have reached a point that the actions are bordering on danger. Now let picture this same situation where a man enters a room with his wife and the Autistic person approaches and carries out his inappropriate action - the consequence might be a bad beating, serious injury, hospital, arrest and so forth. You do not want to see this happen to your own child hence you try every day to warn them with every ounce of vigor you have for their sake.