This one data point may be insufficient to have 100% certainty about the opinion of Brendan Eich, but it certainly is enough for 99% certainty. I'm assuming you are a programmer? ;-) Inside a computer predicate logic works very well, but in the real world probabilistic logic usually works very well, rather than using the rule that after k number of data points your belief suddenly flips over from 0 to 1.
Your first (big) paragraph I do not follow. You did not give any justification for why it's better to get the issue into the Supreme Court ASAP while suffering the disadvantages I mentioned, rather than opposing the ban. The Supreme Court does not just take into consideration the constitutionality in some fixed legal sense. They have the freedom to interpret laws, and they do so according to the current sentiment. Just read the court transcripts and you'll see this. For example they constantly debate whether same-sex marriage will be beneficial to society or not. Since you did not reply to any of the arguments I made, I'll repeat one of them: if there would be a next ban (perhaps in a different state) that is successful, then that will go to the Supreme Court. This is no worse than prop 8 going to the Supreme Court, in fact it's better for the reasons I outlined previously. Do you think that people who are against marriage equality are doing themselves a disservice by donating to anti-marriage equality groups? I really do not understand this, but I'd love to be convinced otherwise by logical arguments.
I certainly agree with the next paragraph where you say that it would be stupid to let a difference in political belief heavily influence your job choice. However, insofar as these differences have practical effects on your treatment, chances of being fired, and mental well-being (it's bad for your mental well-being to be in the closet at work or anywhere else), it is smart to take such things into account.