1.  Non sequitur: failure to meet the objection.  Either give examples of double-blind experiments or demonstrate why double-blind experiments are not necessary.

2.  Appeal to Common Practice: validity is not achieved from 'everybody doing it.'

3.  Argument from Ignorance:  The answer is Yes.

4.  Argument from Authority: There are just as many, as just as good, Authorities (one cited) who object.

QED.

(You see?  I can play the academic game too  ;-)

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre