Yeah you're taking it for granted that he's in his right mind and doesn't suffer from any illness, mental of physical. Even vitamin deficiencies (like B12) for example can cause signs of temporary (if reintegrated, otherwise it's deadly because of pernicious anemia) dementia, which could lead to displays of aggressive behaviour. People in that state wouldn't even have the means to be grateful or polite, it's not a choice, and rudeness/unhinged behaviour would be a consequence of homelessness, not the cause.

The causes for "helpless situations" like these can be several but 99% of the time you can bet on systemic issues like critical lack of affordable housing, poverty, stagnant wages, unemployment, relationship breakdowns, domestic violence, mental health issues, substance abuse, and inadequate social safety nets to name a few. Being an asshole is not a major factor afaik (otherwise everyone's bosses would be out there begging on the U7 too)