Liberalism is premised on the idea that people are inherently good in some sense, and therefore worthy of liberty and equality in some domains. This applies to modern liberals who only care about social liberties and social equality (a.k.a social justice), classical liberals who agree with everything modern liberals say, but they additionally want economic liberty and equality as well. Anarchists can also be considered a type of liberal arguably because the only difference between them and the liberals is that anarchists don’t think there should be an agency which reserves the right to violence in all affairs (a.k.a a state) which is a form of inequality.
The reason liberalism is hard to practice is that there are contradictions between liberty and equality. As people have more liberty, they are free to prefer some people to others for various reasons. This leads to various forms of inequalities depending on the type of preference being exhibited. If the preference is by merit we have meritocracy which leads to people of merit being unequal to people without merit. If the preference is based on race it leads to racism in which some races are unequal to others in certain human endeavors. If the preference is by sexual orientation we get homophobia in which some sexual orientations are unequal to others. If the preference is by wealth we get various forms of inequality in forms of justice, political power, education, healthcare etc.
So liberals resort to various illiberal requirements like enforcement of equality of opportunity (e.g. Social justice extremism, affirmative action) and even enforcement of equality of outcome.
Liberals also end up in a purity spiral in which the more they care about minor infractions of their ideology the greater standing they have in their community. So much like Catholics who avoid condoms are more pious than Catholics who avoid murder, liberals who use preferred pronouns are purer and have a higher standing than a liberal who avoids murder/rape.
BTW this is just the tip of the iceberg when it comes to difficulties of liberalism. For example, many forms of liberalism believe in the ability of laws and lawmakers (a.k.a legislature) to handle all governance scenarios including the foreseen and unforeseen. However, laws cannot work when the unforeseeable happens so even liberals allow illiberal ideas like allowing one individual (a.k.a the president/dictator) to suspend the law, and rule by whim and extra-legal force until normality has been restored. This is yet another contradiction that happens when people try to establish liberal governments. People show this desire for extra-legal heroes in superhero fiction in which one person acts for the good using extra-legal force.