Did you vote in the primary? If you did, I presume you voted for Ginty, who lost. But you don't accept the results of the primary, so you're going to write in his name anyway next November. In other words, you don't accept elections unless they go you're way. Whether or not you realize it, that means you don't accept our Constitutional system.
I can understand your dismay at having Kean be the Republican candidate. If he's anything like his father, I would have a hard time voting for him, too. But in a liberal state like New Jersey (where I was born and raised), the Republican is still better than the Democrat under all but the most dire circumstances.
Life is not about easy perfect choices. It's about making the most you can out of the hand you're dealt. If you absolutely cannot vote for Kean, you would honor the Constitution more if you voted for the nominee of a minority party rather than stubbornly write in the name of a candidate who lost his party's primary.