>it seems to me that there has been a huge increase in violence

So you think that there's more violence because you hear about it on the news/social media, or is it informed by actual statistics? The latter shows a slight bump during the pandemic, but is back to pre-pandemic levels.

>Now I also read about non-US citizens being detained on the border.

The two cases I've heard about both involve people with visa issues trying to cross a land border, with neither side wanting to accept. If you're traveling for a conference and don't have obvious work intentions (eg. interviews lined up) you should be fine.