Sometimes I'd want to agree with you - honestly - but the reason we've not yet adopted methods for injuring and killing people or animals trying to cross the border is because the US has had a long history of understanding the importance of not becomming like North Korea. There are laws against it. That's not stopped the US from supporting numerous murders and conflicts abroad, which is one of the reasons for global migration, but creating a humanitarian crisis at one's border is - well - frowned upon. There is a bill in congress at the moment that would fund additional patrols, deportations &c, and many senior republicans support it, but Trump has told a number of republicans NOT to sign it because he wants to use hatred for his campaign.