Making desperate people less desperate can be pro-social. UBI could drive down the crime rate.

Also you're assuming all paid jobs are pro-social. Is coal mining? Advertising? SEO for MLM firms? Lobbying for kleptocratic foreign governments? Some of these may have some positive effects but may be net negative in their effect on society.

Finally, I disagree that charity isn't a legitimate role for government. Since neither of us is the arbiter of government legitimacy I think we can agree to disagree here.