 We're told that when Imam al-Hussain was a small boy playing in the streets, Prophet ﷺ saw him and extended his arms out, embraced him, and Hussain said something and they made the Prophet smile. And then the Prophet ﷺ said, the famous hadiths, so he said, Hussain is for me and I am for him. Allah loves the one who loves Hassan and Hussain. Hussain was like the, they say the apple of the Prophet's eye, right, just looking at Hussain, put a smile on the Prophet's face and filled his heart with love. This is reason enough to say that all Muslims should love Imam Hussain, alayhi salam.