Context matters. If someone wants to use "trans" as an insult, they will.
"Don't speak to me you trans" and "Don't speak to me you tranny" are both offensive remarks. The difference of using "trans" or "tranny" doesn't change the message.
I'd also like to note that the use of "tranny" is still used self-referencingly by many trans.
"Queer" is an insult where I am from but many homosexuals are increasingly using it self-referencingly ("I'm queer.") and I see less people get all up-in-arms over the word "queer" than "tranny", which I find strange.
It is my belief that giving words power is silly. By fearing them you show others that they can use that word to control you. If you are indifferent, their words fall flat. They become weak and powerless. By advocating the fear of words, you give them increased power. You teach people to fear the word because it can hold power over others. Those who wish to abuse that power will see that and use the word.
In the end you result in the abusers having more power, people with no ill-intent to feel bad for the usage, and people whom the word is targeted at grow more fearful of it. That's a lose-lose for all involved.
By not giving the word an "unspeakable" status - the abusers realize the word holds no power and stop using it, people who have no ill-intent don't have to feel bad for using the wrong word, and the people whom the word targets don't grow to fear the word.
I find advocates of making a word "unspeakable" because it, in certain contexts, can be "bad" is counterproductive is all. You increase the power of the word, nasty people will use it with even more glee, and nothing is accomplished other than self-victimization.
I am 100% sure you can tell the difference between calling someone a t* and calling someone a Jew, and I am 100% sure you know when it is appropriate to identify someone as a Jew and when doing so is othering and degrading.