Every country has borders and reasons to limit immigration in various ways (for example, to certain skillsets). There is no blanket allowance to walk into any country outside of a port. This is plainly illegal. When laws are broken, someone needs to enforce the law, apply consequences, and do so as efficiently as possible. ICE is that agency for the US. I feel like those who think ICE somehow shouldn't exist are simply not being level headed and ignoring the reality of the fact that we are a nation that exists first and foremost to serve its current citizens, just like all other nations.
Lastly, by taking political stances, these companies are discriminating against the silent cohorts in their employee base that do not align with those views. It is an especially big problem in tech companies, most of whom are headquartered in the SF Bay Area or Seattle, two progressive/far-left areas that have skewed politics. Other workers who don't have an issue with the company serving ICE don't have a voice. They have no psychological safety. It is irrational for companies to respond to employee pressure or social media outrage - they should take randomized anonymous polls of their employee base if they truly want a good signal on employee sentiment.