I get that the images of mounted border patrol agents trying to prevent further entry of illegal immigrants is anachronistic; in some contexts it is shocking, especially if you think they are using the reins as whips.
I have not seen any video, I've only seen the images circling. And only after a brief analysis, it's obvious the worst thing photographed is an agent grabbing an immigrant by the shirt, which is hardly damning since their job is to literally stop illegal crossings. I suppose reins could have been used as whips, but it's impossible to determine that from still photos--which is why I suspect we will never see video--because it likely provides contra-narrative context.
We need a realistic immigration policy and sane immigration rhetoric from both parties. Somewhere between open borders and amnesty for millions (or some Orwellian synonym for "amnesty"), and total isolation is probably where it needs to be. I would even support allowing hundreds of thousands of skilled AND unskilled immigrants from virtually all countries if they pass reasonable background checks, but that has to come with better security, better rhetoric, stability and predictability--we can't just significantly change the law every other year or we'll continue to have humanitarian/immigration crises.
The previous paragraph is fantasy. You know that right? I will continue to support such a policy or one close enough to it, but the big ugly wall is more realistic. Build the wall.