Well, we've already crossed that Rubicon, haven't we? We already have the ability to choose a child's sex as well as eye color, why not offer a checkbox that says "more muscle and strength?" Unsurprisingly, we as a race, have the moral flexibility to be OK with this.
Keep in mind, that muscles may not always be fashionable. In some not so distant, Wiggs-n-Falconian dystopia, muscles might be for the "laborers" and the fashionable political and media elite (our "betters") would be thin as rails.