It is said by the Prophet SAWS that Allah SWT loves His creation more than a mother loves her child. We enjoy many blessings that are the result of this divine love.
This life is a test.........it would hardly be a TEST if everything was all rosy and wonderful and just peachy. What makes this life a test it that we have been given the free will to do what is right or do what is wrong. We have been give the free will to use our intellect and emotions for the betterment of mankind or for our destruction. There is hadith which states that shaitan, who is the root of all negative emotions (anger, hatred, pride, jealousy, greed) runs through our bodies like blood. That is why there are surahs and duas, which we recite to seek refuge from the detrimental affects of shaitan.
Plus in the Quran (surah Rahman, for example) Allah urges us to look around us and contemplate the blessings that we have been provided, which are a sign of love mercy. So, yes, love is a fundamental part of creation. But still we are not devoid of negative emotions. Some of us can control them better than others.
Why are criminals oblivious to love? There are many factors that can contribute to this. Perhaps they simply choose not to see it. Remember, you are given free will and intellect. And not everyone chooses to use it the same way. Perhaps these criminals had a dysfunctional childhood. Maybe their parent/s were dysfunctional role models (alcoholic, verbally/emotionally/psychologically/sexually abusive, controlling). It's tough to break out of the vicious cycle of an unhealthy upbringing. Those that manage to succeed and not repeat the same mistakes had overcome many mental roadblocks before they could begin to heal. The best thing that parents can do for their children is to provide them with a nurturing environment where they develop a healthy self-concept/esteem. BECAUSE PEOPLE WHO HAVE A HEALTHY SELF-CONCEPT/ESTEEM RARELY GO AROUND DELIBERATELY HARMING OTHERS.
It could also be the company that one surrounds him/herself with. And even circumstances such as poverty can lead people to lose faith in their deen and human relationships. Desperate situations lead people to desperate measures. A person, in order to escape poverty, might resort to drugs, corruption, etc. But those individuals who are strong in their faith and believe in love for their fellow human beings.........will be able to overcome their LOWER NAFS and the insinuations of the shaitan.........and do what is right.....even in the most desperate of situations.
It is said that every child is born a Muslim, fee of sin, pure, open to guidance and a proper upbringing..........but it is the parents, the upbringing, and environment that make him who he is. I remember hearing/reading this in either an Islamic book/class, can't remember.
So, it is not that simple for everyone to believe in love and have faith. Way too many factors play a role in a person's beliefs. The best way to bring someone back to the right path is through your actions. Yes, dawa can help. But actions speak louder than words. Sometimes the people who have the most toxic attitudes are the ones who need our love and affection and care the most. But it takes effort on our part to put our offended egos, pride, and bias to the side and show them that love and be a positive example. Islam is a religion that attained many followers because the Prophet SAWS showed them the right path through mercy, kindness, and a gentle manner.