Bass, while I pretty much agree with you, I am not sure you can call Parmenides and Gorgias both sophists. Parmenides (thinking and the thought it is are the same) seems more a philosophical metaphysician and less a rhetorical teacher of virtue. It is certainly debatable though.
Fair point. The overall idea is the same. Plato is not universally opposed to all sophists (though he may be philosophically opposed to their practices).
1. It doesn't matter whether Plato was opposed to sophists or not, what matters is did he give an accurate portrayal of their beliefs.
2. We know that neither he nor any others can be relied upon to give an exact replica of what the sophists believed.
3. We simply cannot know with any degree of certainty what they believed without their writings.
Heck, I can't figure out with any degree of certainty what PLATO believed and I try to re-read at least one dialogue every month! The point of philosophy is to change your world not to understand how the sophists interpreted theirs (which apologies to Marx).