I happen to agree with Kate's politics and think it is certainly OK to update fans about what she's doing and even why she feels the way she does. But urging fans to vote for a specific candidate is not proper.
Those of us who are Kate fans aren't surprised by her views (or the fact that she can't stop herself from expressing them!), but this was a huge con with fans of many other Trek stars, who probably didn't expect to or want to hear one of the actors to ask them to vote a certain way.
Susan Sarandon, Tim Robbins, Sean Penn, and Martin Sheen are also actors I admire, but I don't think they should use the Acadmeny Awards Ceremony, or other venues, as a platform for their views any more than Kate should use a convention to celebrate Trek as a platform for her politics.