I will judge the business owner as prejudiced - but it does not make it ethical to send armed men forcing them to trade money for labour with Irishmen. Government laws in the end require enforcement, otherwise they are just nice words. It’s not moral to force someone do act against their will, even if they are unfair, as long as they themselves are not using force against others.
The same principle holds for borders and other forms of property.
Issues of right and wrong often are issues or greater vs lesser evil.
The fact that you pose this question admits the political nature of these cultural conflicts. There are multiple avenues of resolution, some which involve government, some don't. We're all welcome to have differing opinions on how to deal with them, even if we can come to agreement on common values.
The same principle holds for borders and other forms of property.
Issues of right and wrong often are issues or greater vs lesser evil.