Don't get me wrong...I've had chorizo in paella, and it's delicious. The paella tastes more like ... well...chorizo. Not chicken, not seafood, chorizo! Not only is chorizo paella not even a dish in Spain, but if i'm going to have anything chorizo-flavoured, it's chorizo. (how many times can I say...Chorizo!?)
As for the paella, I know a good paella by the taste of the rice itself, infused with spices, chicken, meats or seafood stock used. Sometimes less is much more.
So basically, using chorizo is a cheat's method (no judgement) of flavouring up a paella in lieu of a decent stock.
IF you are spending quality ingredients and time in developing an amazing stock - why add chorizo to simply overpower your delectable creation?
IF you aren't creating an amazing stock - chorizo away. It will be eaten.
My recommendation though is to have your chorizo solo, as a Spanish tapas, with crusty bread and lemon. Then, enjoy your paella and enjoy the subtlety of its various flavours.