How to dismiss an opponent

In "The Blind Watchmaker" Richard Dawkins makes the following two statements:

1. "No serious biologist doubts the fact that evolution has happened..." P. 287

Now complete the syllogism:

X biologist doubts the fact that evolution has happened
Therefore X biologist is not a serious biologist

Result: I don't have to give any weight to X biologist's arguments because he really isn't a serious biologist. He is dismissed.

2. "Modern theologians of any sophistication have given up believing in instantaneous creation." P. 316

Now complete the syllogism:

X theologian believes in instantaneous creation
Therefore X theologian is not a sophisticated theologian

Result: I don't have to give any weight to X theologians arguments because he really isn't a sophisticated theologian. He is dismissed.

Presumably the argument would continue:

3. No serious physicist ...
4. No serious chemist ...
5. No sophisticated philosopher ...
6. No serious geologist ...
7. No self-respecting dentist ...

What is wrong with this line of reasoning?:

False premise.

It is not possible to evaluate the seriousness or sophistication of someone's thinking based on one simple litmus test. The universe in which we live is just a little bit more complicated than that.