The relevant metaphor here is "killing the goose that lays the golden eggs". A country with pro-prosperity policies is a goose. Filling it with people who haven't assimilated the memes of the people who pass such policies will arguably lead to the end of this wealth production so sought after by immigrants.

Arbitrarge doesn't kill metaphorical geese like that: it simply allows people to get existing gold eggs more efficiently. It might destroy one particular seller's source of profit, but does not destroy wealth-production ability that an immigrant-based memetic overload would.