Am I presumed "fit" in regards to my visitation and custody rights, unless good cause is shown and proven otherwise by competent, substantial evidence?

Is there a law that says I cannot have visitation and custody without a guardian ad litem or a psychological evaluation to determine fitness?

The natural parents of a child are presumed fit in the absence of evidence to the contrary. Alas, what passes for evidence that may upset this presumption is largely a matter of local law and custom and the proclivities of the judge. And judges are famously known to be full of proclivities.

Generally, it would take what is known as "substantial competent evidence" -- evidence that would be admissible in court -- to strip a parent of his or her rights. However, it's easy for a judge to find that just about anything constitutes "substantial competent evidence." One famous judicial test says substantial means "more than a scintilla" -- although one person's scintilla may be another's boatload. This, too, is a standard that is difficult to put on a spoon and bite.

Once the judge has "evidence" of unfitness, he or she can order an evaluation and a guardian ad litem.