"Alt-right" ideas are growing in the US because they reflect reality. Not because of some nebulous "hatred" or simple ideological preference. They are growing due to structural factors. As long as those factors remain, alt-right ideas will become more appealing to more people. A very brief summary that will explain a lot if you are honestly curious about all this stuff:
1. The US is becoming more socially-fractured over time.
2. One major cause of this is due to the rapid shift in American demographics in recent decades
3. Demographic shifts often lead to instability - this is a simple fact of history
4. They lead to instability because groups with disparate habits, behaviors, cultures, and outlooks compete with each other for resources and naturally clash over their differences
5. These differences are influenced to some extent by biology/genetics, meaning that they are innate and not subject to total modification through "social engineering"
6. Not all groups have the same demonstrated capacity to build or maintain advanced modern civilizations
7. Demographic change in the US has increased the population from such groups, leading to greater strain on the shrinking functional portion of the population
8. This will all naturally lead to social tension and possibly conflict
9. None of this can be wished away by people impotently calling for "civility" - it'd be nice if it could, but we are realists
None of this is difficult to understand if you are willing to face actual facts and think about it for a moment.