As long as it does not affect me in a negative way, I wouldn't have any problem with it. The only time I might get mad is if I were to lose an empty coach seat next to me and thus lose all that extra room to spread out. When I am in MCE, I can usually tell if someone was randomly assigned an MCE (not a poacher in this case) ends up in the seat next to me. (they are often in a middle seat). I always make polite and discreet conversation and make sure they know they can have a free drink if they want it.