I'll play. I realize reasons to me might not be to someone else.
1) I don't expect the Tonale to sell very well in the US with the Dodge undercut, so you won't be seeing yourself at every stop light. In a few years I'd bet it will be the most often seen Alfa though.
2) The Tonale will not have whatever hidden de-contenting/cost cutting that has taken place to make the Dodge so much cheaper.
3) The Tonale is better looking despite some obvious similarities. You will also only be able to get the gorgeous 5 hole wheels that scream "Alfa!" on the Tonale.
4) While depreciation on neither brand is great, the Dodge will be worse percentage wise.
5) After the initial splash, advertising on the Tonale will likely be non-existent if Alfa follows past marketing habits. A bit down the road the Tonale will likely be able to be had at a decent discount, putting a dent in the price gap.
6) It's actually an Alfa. Researched, designed and built by Alfa.
7) You'd have to buy a Hornet at a Dodge dealer, then look at the Dodge badge the rest of the time you owned it, I'd bet in a short time you'd wish it was an Alfa. Don't see anyone enjoying the exclusivity and fun of the Alfa culture being long term happy with the Dodge.
I'm personally still not happy about the Dodge thunder stealing and I could probably come up with some pretty good reasons to buy the Dodge too though.