If that's the freedom of expression then everything else which follows is governed by the universal rule of freedom of reaction. Atheists themselves are ideological radicals/ extremists who do not accept alternate narrative.

Another important point is they miserably fail to distinguish between Abrahamic ideology and what is called dharma which has more than twenty-seven sects including the one which is dedicated to atheists.

There's a fundamental problem with the whole western concept of atheism. For them, atheism means mockery of all the religions with a slight more emphasis on Hinduism and insulting its followers.

There's a convenient orgy between leftist atheists and ex Muslims who have left Islam but the Islamist within them stays alive which comes out from time to time and their hatred for Hindus and Hinduism is more than for the religion they left.

In contrast to what has been said, atheists also have a tendency to be more violent. They think religion & faith are the root cause of all the problems & it's a moral obligation of atheists to eliminate both & hypocrisy is unparalleled. The so-called champion of Modern Atheists.

Atheists think they are more rational than others just because they believe in science which is a subject of check and measures but research says something else about them. (Refer to the pic and the link attached with them) https://phys.org/news/2018-09-atheists-rational.amp?__twitter_impression=true

There are multiple reasons behind this behavior and that depends on the country the atheist belongs to and his religious background. It is not a simple argument/ debate. Geography and religious background play the most important role.

For example, a so-called ex Muslim from the subcontinent is likely to insult Hindus and Hinduism more than other ex Muslims from the Middle East or some western countries. The same goes for Christians from the subcontinent and Western countries.

Political alignment plays an important role. A leftist atheist from the subcontinent is more likely to insult Hindus and Hinduism than non-leftist atheists and again the geography & politico-religious background matters.

Atheists from Hindu & nationalist political backgrounds though can be unconditionally atheist but they won't target Hindus, Hinduism & the gods/ goddesses (in general) but it changes when you encounter such atheists from different geography. So it's complicated.

At the end of the day, it has got everything to do with their mental satisfaction which is mental sickness. A mere feeling that their statement is hurting the sentiments of Hindus gives them immense mental satisfaction and this is what motivates them.