Type 3 seems to get a bad rap because of their chameleon-like ability to take on the identity valued by whatever group they're trying to become a part of. Three points I'd like to make about this:

1. Not all type 3's have this tendency. It's more a part of the 3w2 than the 3w4.
2. The position that this is deceitful doesn't take into account the type 3 perspective.
3. Being yourself doesn't require that you be the same person in all situations and circumstances.

To take on an identity valued by the group, all you need to do is dress the part, walk the walk and talk the talk. When in a corporate environment, put on the suit and play the executive. When on a construction site, make sure you scuff up the new tools so that you don't look like a rookie. Each group has their way of talking, acting and thinking.

It doesn't feel like deceit when you look around, see what the situation calls for and simply adapt to fit in. It's an important skill to learn when going for job interviews, getting along with people, and generally learning how to sell yourself in order to get where you want to go in life.

However, some people are of the belief that you have to remain authentic in some way - that by simply adapting your self-presentation to better fit the situation, you're somehow selling out your true self and being deceitful. The unspoken assumption underlying this belief seems to be that there is a you that's independent of your environment - that there is some self that existed in the past, lives on into the future and must be kept true to in the present.

If who you are changes or adapts to each situation and environment you're in, you're sense of self is inseparable from your environment. It's not that you don't have a self, it's more that who you are is not independent of the world around you. There is little separate sense of self, but greater collective sense of self.

With all that said, the danger comes in when the presentation goes too far. When self-presentation goes beyond reality, that's where the deceitfulness can appear. It's not the presentation, it's going too far with it.