On March 15, a gunman killed 50 people, and injured dozens more, at two mosques in Christchurch, New Zealand. The attack, which was the deadliest in the country’s recent history, was made even more horrible by happening near the time of Friday Prayer, one of the central rituals of Islam. While the investigation into the shooting is still ongoing, the alleged shooter reportedly wrote a manifesto espousing anti-immigrant, anti-Muslim, and white supremacist beliefs.

That same day, in the US, President Donald Trump continued his efforts to build a wall between the US and Mexico, vetoing a Congressional resolution that would have blocked his declaration of a national emergency along the southern border. Such a wall would fulfil his often-stated campaign promise to reject immigrants who ostensibly threaten the country’s “security,” immigrants about whom the President has spoken in disparaging terms, using an expletive to refer to countries with predominantly nonwhite populations and calling undocumented immigrants “animals.”

Is there a common thread that ties the President’s effort to build a wall on the southern border of the US and an unspeakable act of violence in New Zealand?

I would argue that that thread is hate, and, in particular, hate for “the other”.

Hate often manifests first by targeting “the other;” undermining the health of marginalized communities like immigrants, people of color, and the lesbian, gay, bisexual, and transgender (LGBT) population. For example, state laws permitting businesses to deny services to same-sex couples were linked with a 46 percent increase in mental distress among this population. In the racially-charged aftermath of the September 11, 2001 terrorist attacks, Arab-Americans who encountered discrimination experienced a rise in psychological distress and poor health.

Racism has been linked with poorer mental and physical health among African Americans; for example, perceived experiences of racism may be linked with a higher incidence of breast cancer among African American women. And anti-immigrant stigma, fueled by rhetoric and political policy, can widen health disparities among immigrants—and the citizens of color sometimes conflated with immigrants due to stereotypes about race and citizenship—by generating stress, increasing the threat, real and perceived, of violence, and making it more difficult for immigrants to access needed government services.

But hate is not just a problem for “the other.” It threatens the health of all. In recent years, we have seen how hate has created the conditions for acts of violence in the US, from the shootings in Charleston and Orlando, to the attempted bombings of political figures, to the Tree of Life synagogue shooting, to the ongoing challenge of school shootings. When someone who has been twisted by hate chooses to commit mass violence, everyone is a potential victim. This is especially true in an age when new technologies help spread toxic ideologies around the world, demonstrating that hate is a global problem, which we, as a human community, must address.

Hate can also distract us from the actions we need to take, at the political level, to ensure our society is as healthy as it can be. In the US, for example, opponents of government initiatives like welfare, public housing, and the Affordable Care Act have long argued that such programs only benefit the undeserving, making clear, through coded and sometimes not-so-coded language, exactly who they consider the undeserving to be—typically, immigrants, people of color, and the many financially struggling Americans too-often slandered as “lazy” by those who would deny them assistance.

Yet a country with universal health care, a robust system of public housing, and help for the economically imperiled, is a country where we can all be well, not just members of a particular socioeconomic group. Creating such a country means first addressing hate.

Having said this, in our polarized era, it is important that we recognize the distinction between the words of prominent politicians and the blood spilled by violent extremists. We should be careful about suggesting a connection between the President’s calls for a wall in Mexico, his broader rhetoric about immigrants, and the shooter’s actions in New Zealand. Yet to ignore the link between words that promote bigotry and hate and the crimes to which they can lead would also be to ignore honesty and common sense. Words matter. Culture matters. When we tolerate hateful rhetoric, we risk creating a culture from which hateful acts can emerge.

This suggests the need for all citizens, including the President, to work to minimize hate. This will not be easy. Hate can be hard to look at. It is often either a sight too ugly to stand, as in New Zealand, or too well-hidden to fully see, as in its influence on the political policies that shape our lives. But we must look at it, if we are to move past hate on the way to a healthier world.

In a sense, the wall we have heard so much about has already been built—it is the barrier of hate that stands between where we are and where we could be, between health and disease, between finding solutions and settling for scapegoats. It stretches all the way from America’s southern border to the bloodshed in New Zealand.

Tearing down this wall means rejecting hate. To do so, we must name hate when we see it, counter hate speech with a language of compassion and solidarity, and oppose violence in all its forms. We must call attention to when politicians ignore our better angels and choose, instead, to play to our worst instincts. And we must embrace the most effective antidote to hate: love.

Sandro Galea, MD, DrPH, is Professor and Dean at the Boston University School of Public Health. His latest book, Well: What we need to talk about when we talk about health, will be published in May 2019. Follow him on Twitter: @sandrogalea