Atheists believe that everything is an accident

Religious people like to say that atheists believe everything is an "accident". But an accident would require a mind in the first place, which had intent. So by saying that atheists believe everything is an accident is implying that atheists believe in a designer, who strayed from it's intent, which is clearly not the position of an atheist, by definition, who does not believe in the existence of any deities that had intent or made an accident.

If there are no gods, then our existence is neither accidental or intentional. It just is. We are the ones who are speculating on whether it's an acccident or intentional, which is irrelevant because from what we can tell, our existence is not the result of a sentient mind.

What are your qualifications?

This is the fallacy that if someone has not studied or been educated in a particular topic on a high enough level, then that person not allowed to criticize that topic of interest at all.

It is deemed a fallacy for the reason that information is legitimate or illegitimate without needing the person stating it to be an expert or even authoritative. If someone is an expert then they may know more on the subject, may be more likely to be correct or be more believable, but that doesn't discredit the information.

Why can't everyone just have their own beliefs?

Everyone does have their own beliefs, but all beliefs are not equally valid nor do they equally reflect reality. An incorrect belief may occasionally be harmless, but it can also directly result in negative consequences (unnecessary guilt, bigotry, racism, oppression, strife, silencing of dissent, the death of the innocent, etc.)

Beliefs direct and guide our actions, and incorrect beliefs can lead to actions that increase harm, both for the individuals holding a particular belief and those around them. A perfect example of this is the preventable deaths of children at the hands of those who wait for a god to heal instead of taking their children to a doctor. If someone dies because their faith kept them from seeking medical treatment, it is tragic. It is far more so when an innocent child is lost due to their parent’s ignorance and their reliance on a belief that is not supported by logic, evidence or reason.

Another example of beliefs harming others is the oppression and hatred directed at homosexuals, atheists and others.

A belief or opinion that is based on lies, falsehoods or misunderstandings will have consequences. It is better that our beliefs and opinions reflect the world around us, and it is often necessary to change our beliefs as new evidence becomes available.