Take the example of a Scotsman. A Scotsman is defined how? By being Scottish, of course. No action makes one a Scotsman, nor does any action disqualify one from being one. One is not a Scotsman by choice but rather by birth.
Conversely take the example of being a Socialist. A Socialist is defined how? By Socialist beliefs and actions. One is not born a Socialist but rather makes a choice at some point to be one.
Hence saying that a Socialist would not endorse the Health Insurance Industry Bailout Act of 2010 (or "Obamacare" as some like to call it) is not a No True Scotsman argument, it is a statement of what a Socialist is . Similarly saying that a Socialist would not sign off on extensions of the world's most regressive system of taxation is also a statement of what it means to be a Socialist.