While more than half of Americans rejected socialism in a recent Gallup poll, 43% surveyed said some version of it would be good for the country. That sentiment was held by 58% of respondents ages 18 to 34, compared with just 36% of those 55 and older.   Americans who came of age during the last recession often embrace a larger government role in social policy. They cite stagnant wages, student loan debt and a decrease in employer-sponsored health insurance and pensions. Younger Americans are less threatened by socialism than older generations, who might associate it with Soviet or Chinese rule.