As for being RIF'd for selling shares on the day they vest...the corporation can't make inferences like this. How does corp. know that employee didn't just buy a house and needed the grants to help make a down payment or other purchase. I have sold my shares on the day they vest for well over a dozen years at Symantec and not been punished.
FYI - at least under US tax law your getting taxed for shares the day they vest anyway as W2 income. There is no real value in holding shares. For comparison, if you sold shares the day they vest, then bought back same shares on the open market at same price and held for a year, you would get taxed the same. On the other hand, if you bought shares in another company with equal or better growth prospects, you would be diversified and better protected.