Certainly there's all kinds of evidence for elevated risk of nervous and mental issues in adopted children although the earlier they are adopted the less the risk, but elevation still occurs.
When you used the word "often", what exactly did you mean?
I'll admit that adopted children have factors that make them more likely to have mental issues, even minor ones. But I think what twigged me to that sentence, even though I didn't recognise it consciously at first, was the use of the word "often".
It makes me think "50% or more of the time".
If you mean that adopted children have a slightly higher risk of being screwed up then I agree, although I don't think your original choice of words was fantastic.
If you do mean that a significant proportion of adopted children are screwed up, then I'd be interested to know what constitutes screwed up and to see something to support the claim. Maybe it's true, but it feels a bit weird to me.
Well, that gets a little facetious and I'm not sure the evidence you mention exists.
The evidence that I was meaning was the previous sentence. Adoptive parents have to go through all sorts of stuff before they can actually adopt a child. Someone who cares enough to do that has displayed significant interest in being a parent. Colloquially, they give a ****.
You cannot accidentally become an adoptive parent, it is a planned and deliberate action, with many chances to back out.
Normal parents on the other hand, can have children simply by being unlucky. Failure of condom quality control, whoops, you're pregnant.
The vast majority of "normal" parents almost certainly do not fit this profile, but there are a small amount that do. These are people who potentially have no interest in becoming parents, nor the resources to do so, but end up stuck in a bad situation.
It was written in an entertaining manner, but I stand by the sentiment.