Ridiculous??? I hardly think it is "ridiculous", I just think the flavors of Belgian Candi Syrup would remind me of a Dubbel, not a porter. Just like the raisin character of Special B stands out like a sore thumb in just about any non-belgian beer, to me at least. Doesn't matter what recipe it is in, if I taste special B I immediately think "belgian".
And, historic beers are kinda silly. Just because something was "historically" brewed one way doesn't mean it works today. Historically all beers were smoky and sour, that doesn't mean we should necessarily emulate that today. And if you wanna talk "histororic" I hardly think Porters used Belgian candi Syrup. That's not "historic" at all!
If you wanna add some sugar go with molasses or something that won't remind you of a belgian beer. That's my take on it, my recommendation - not cut in stone, not the arbiter of all things, but hardly "ridiculous" either.
Sorry I'm going to stick with “ridiculous.” I'm trying not to be combative here, please don't be part of the trend to slap down any ingredient that doesn't fit into the cookie cutter definition of what a porter (or any other style) should be. Styles are born from experimentation and imagination.
While I don't personally use special b in my porter, it shows up in a ton of porter recipes. Don't forget that your palate doesn't represent everyone's, just as mine doesn't.
What flavors come from candi syrup? Let’s see; clear syrup = flavor neutral, amber syrup = mild caramel flavors, dark = vanilla/plum/raisin, dark2 = burnt sugar, figs, ripe fruit, toffee and dark chocolate. There's a myriad of flavors to be had from the caramelization of sugar. I don't see any problem whatsoever with mild caramel, vanilla, burnt sugar, toffee or dark chocolate flavors in a porter. The remaining flavors (plum, raisin, figs, and ripe fruit) in that list could just as easily come from fermentation byproduct (unless you're a wlp-001 fan). I see plenty of room to add the syrup(s) without getting the raisin flavor.
You keep throwing around the phrase "Belgian candi syrup" but Belgian candi syrup is just sugar - like the sugar you add to your beers except that it's been caramelized. I can take table sugar and make "Belgian candi syrup" on my stove. Molasses is a by-product of sugar processing and while I personally think it's disgusting in beer, I guess I won’t say that you
can't add it to your porter if you like.
In reality the "D2" syrup flavor should be an excellent approximation of the sugar that they would have historically added.
Seriously - I'm not trying to be combative.
edited to change the can to can't