I personally have no problem with synths. As with any instrument, it's a case of using them in such a way that is appropriate to the arrangement. Just as the material on Shangri-La doesn't generally lend itself to electronic sounds, synths work brilliantly on many of the songs on On Every Street and both albums, though totally different, work just as well for me. They can add a lot of depth to a song and utterly transform it and of course the pallette of sounds is pretty much unlimited!
I've deliberately avoided hearing any snippets from Privateering (other than Redbud Tree) as I don't want to spoil listening to it when it comes out, but I'll be interested to hear how much synth activity there is on there. MK has been gradually bringing them back in since Kill to Get Crimson. The gentle synth pad you can hear at the beginning of The Car Was the One is subtle but very effective.
How much synth activity on Privateering? Not much, fortunately! The only snippets with synths seemed to be Redbud Tree (the pling-pling thing), Privateering and The Dream of the Drowned Submariner.
I agree that the synths kind of work on On Every Street (and what a great album it is), and The Car Was the One is one of my all-time favourites - in spite of the synth work. Still, I believe that great songs like that one would have worked without synths easily, an maybe even better. Privateering is the best example so far: The synth at the end is nothing but disturbing to me, completely useless. And worse: It kind of destroys the "handmade" feel the song has.
My problem with synths is simply this: They're a cold, dead thing. No human touch, and that's what I miss. Of course, if you WANT to make music that sounds sterile, cold, industrial, whatever (and I'm not saying that's necessarily a bad thing), then synths will be very helpful. But that's just not the corner Mark is in these days. He's music - as far as I can tell - is all about authenticity, if you will, it's handcrafted, warm-hearted, very "human". I just don't see how the synths fit in here. If he uses them occasionally, they sound like an awkward left-over from the 80's.