Something to remember.
In many cases, pursuit of EGI correlates with proximate measures that increase fitness, so no altruism is involved. After all, why is pro-immigration and pro-refugee activism termed as (pathological) altruism? Keeping out immigrants can enhance wages - selfish! Keeping out immigrants allows for more space and better schools and neighborhoods - better for family formation - selfish! Ethnocentrism is selfish, not altruistic. Will free-riders take advantage? Sure. But what about immigrant free-riders taking advantage of the open-borders altruism of the native population? That's s double blow - less overall genetic representation AND decreasing "alleles for altruism" by allowing selfish free-riding immigrants to prosper at the cost of altruistic "let them all in" natives.