Language is an abstraction. We're not very good at processing tons of binary code rapidly (that would truly be tl;dr), so we need more abstract things to transmit our ideas. That is why we don't just use numbers.
People are also inherent lazy, so they must pick the most direct and easiest way to get these ideas across. Just take the internet where we seem to constantly find shorter ways to type things. It's also easier for me to say "Fuck you" then to write a 30 page essay about why someone sucks.
Different words can have similar meanings, but the ability to attach meaning, emotion, and intent can make them all useful. Big words are not just to sound intelligent but to reach another level of precision with the idea you are trying to imply.
To convince others, you should avoid using especially strong language such as "trash". It's best to know your audience in all cases, and to adapt your language to pander to their sensibilities. Remember you can express the truth in many different ways without actually lying. It's why we come up with shit such as "Collateral damage". In the ethical sense you should avoid these tactics. Also, don't waste people's time. Don't prefix sentences with "No offense" because they know you are bullshitting them anyways.
