Well, probably it's the way that we deny the truth that causes
us to act out bad thoughts and hence punishment in hell as a
result.
I do not know if you are a Buddhist, but it is recorded in
scriptures and related discourses that any form of bad deed done,
be it carelessly or deliberately, be it by thoughts, words or
action, yields negative karma.
It is not for me to say whether any ignorant person who slanders
buddhism by thought, mouth or deed will or will not be given
another chance. I was just quoting the scripture as it is and the
mentioned verse explained in great details of what happens to those
who have only slandered in their mind, not necessarily through the
mouth or deeds.
The Bible clearly mentions that those who commit adultery in their
mind would have been deemed to have committed adultery in spirit
and hence committed sin in the eyes of God.
The above, I believe, is a rather common teaching in most world
religions as to the effects and consequences of one's thoughts when
relating to the God in their beliefs. Although there is no God in
Buddhism, the general principles and rules apply.
My post was to discuss the gravity of the consequences of
slandering and to explore other scriptures preached by the Buddha,
whether such ignorant people are indeed doomed for eternity, for
repentance or any salvation methods is not specifically mentioned
after that verse or at the end of the sutra. However an important
note is, repentance is always implied in all Buddhist
teachings.
Exactly when and how those who have slandered the Dharma or any
Bodhisattva or Buddha will be delivered from such severe and long
term suffering is really a restricted domain of knowledge of the
Buddhas.
I have quoted the Lotus sutra in page 1 of this post which
mentioned that after a long time of suffering in the 3 evil realms,
those who had slandered the Dharma or a particular Bodhisattava
will eventually be
delivered by the Bodhisattva who they have slandered against.
I also agree with you and believe that eventually everyone will
realise the Truth on their own in their own time.
There is always hope for all of us, for all sentient beings have
the Buddha nature in them. 