Yah, the safest way is not to judge actually. We never really
know what others are really thinking - they may have the most
sinister or altruistic intentions - we can never be sure, and
there's really no point judging.
But what we do know of is that everybody wants to be happy - though
everybody's interpretation of happiness and the means to gain
happiness may differ, we all want to be happy in our own ways. That
"wanting to be happy" is an indication of the presence of Buddha
Nature in all of us. And this, I believe, we should learn to
appreciate; and the more we appreciate that, the softer and less
critical we become of the good and bad behaviours of people around
us.
Even for people who pretend to be kind (actually, like what you
say, most of us are like that - we more or less always have
self-serving motivations, which is why we're still trapped in
Samsara), well, sometimes I think that it's good that they're
trying to be nice, or at least trying to appear nice. This shows
that in their minds they know what are the better qualities, even
if they may not have the conditions to be genuinely kind at the
moment. Well, at least these people are spending time and effort in
pretending to be good people; at least they're not spending time
and effort in making and planting bombs...
True, indeed the safest way is not to judge. But don't you think
it's very frightening, these very people pretending to be kind and
all that, and you trusted them almost completely, and poff, you
don't know what hit you, you lost your job, or your performance
review gets the worst grade in all working years, and you STILL
think that guy is a kind person becos he has always been kind and
helpful to you....
Though they are not making bombs, but they are creating bombs of
distrust and manipulation...that is invisible killing....
But still I wish to say I understand your intentions and main point
here, to be less critical. But I'm a mere human, I have needs too
before I attain the Diamond Sutra's level of perfect non-ego and
non-attachment.
It's just so unfair to be less critical on people, but critical on
myself thinking "oh dear, I must have done something to deserve
this", or "it's not his fault, it's my fault"...
I'm just so afraid, that not thinking about good and bad
behaviours, makes me a zombie. I just trying to numb myself into
not thinking about good and bad behaviours...I'm afraid I might
become indifferent and uncaring about myself and others...
No. For now, we can only just imagine. Then researching and
trying to get more information about the top of Mt Everest and its
air(by studying/listening to the Dharma), by analysing and
continually checking and questioning about the routes to Mt Everest
(by contemplating over and over again what we learnt from books and
sermons), and practicing and rehearsing over and over again
climbing the mountain - and eventually really engaging in the
actual climbing (by doing meditation regularly and diligently, and
eventually actualizing the meditation itself
Wow, you are good at relating to and explaining such examples.

Rightly as you pointed out, big and small are relative. There's
no 'big' truly existing separately from 'small' and vice versa.
Whether big or small, like what you say, "no big deal". Just as
when your right hand scratches your left hand to relieve its itch,
your RH doesn't think it did anything big or small to help LH, no
big deal yea?
Nope, not entirely no big deal. My RH wouldn't think because my
consciouness is the only 'thing' that can think. IF my RH scratches
my left hand, obviously it's no big deal. But when there's a need
to use either of my hands to scratch the itch of others who ask of
me, then it's not easy for me to think it's no big deal.
Cos some will say "scratch harder", some will say "use so much
force for what?" And some will say "scratch longer leh...."
If you know what is "not sincere", you are probably quite close
to knowing what is "sincere". At least you have a vague idea of
what that is. Yet due to our temporary defilements, we do not
really know what is truly beneficial for others, nor do we really
know how to engage in beneficial actions. For now, what we can do
is really limited - though that shouldn't stop us from helping
beings in our currently limited ways. That's why we should try to
generate the motivation to become Buddhas ourselves - not just for
our own sake, but really so that we will have the wisdom and
skilful means to be truly able to benefit others.
I agree with you that we should help others within our current
limited ways. I don't know, I just feel so fake, feel so
useless...