That they know the commonly accepted definition of racism, and that they insist on using another. To be lazy would be to use the common term and not think about it. It takes some thought to use a secondary definition, especially when you know people will confuse it for the more common one. This isn't an oops-didn't-think. This is a deliberate choice of words.
Laziness is a spectrum. The laziest option would be to not bother promoting a political agenda at all. For examples elsewhere on the spectrum, see your two examples of rhetorical strategies below. The former is less dichotomous, less simplistic, contains more qualifiers, and requires extending empathy and diplomacy to others with no guarantee that one will receive it in return. It is a more cognitively and emotionally laborious strategy to undertake.
A person who uses a less common definition of racism is not necessarily going out of their way. That it's less common among the general population doesn't entail that it's less common within the circles with whom the speaker associates. It may well be that they disagree with the common definition, just as many of us in the atheist-sphere disagree with more common definitions of "atheism", instead preferring the "absence of belief" definition. Sticking with one's personal lexicon rather than trying to match someone else's usage is very much within one's way.
I've experienced this myself in non-political contexts-- the popular terminology may reflect popular misconceptions, and it can be prohibitively costly in terms of time and effort to express my ideas clearly and coherently without unpacking the assumptions built into the popular terminology and introducing unfamiliar jargon. At times, I've given up on trying to make myself understood by as many people as possible, and simply defaulted to speaking the way that I think and hoping for the best. The alternative tends to result in very long posts.
The previous paragraph can be expressed more concisely using unfamiliar jargon-- it's difficult to communicate with people across a wide
inferential distance. That's probably why you may often see social justice enthusiasts try to make you follow links to educate yourself in what they're talking about, instead of explaining it to you themselves.
Do you have any idea what strategy could be employed to prevent such distractions?
Yes. Acknowledge it and move on. Making a show out of avoiding it, pretending it doesn't exist, and redefining common words so as to exclude it, is making a show of it.
Compare this:
"Tribal impulse and us vs them thinking happens to all of us. It is something we should try to be aware of and control within ourselves. When you add centuries of power imbalance to it, and when it gets ingrained into the very customs and systems of society, it is especially potent. It becomes part of the institution. We should be on guard against that especially. Even if you yourself are not a prejudiced or bigoted person, you can still benefit from such an institution. This is what people mean when they say "white privilige" in America. It doesn't mean there are no privileged black people or disprivileged white people. It means that all else being equal being white has benefits over being black..... and this is how [insert examples and research]... and this is what we can do about it.. [insert your ideas]"
To this:
"Racism and white supremacy are cancers in our society. If you are white, first admit it in yourself. Stop participating in it. Admit you benefit from white privilege, and then listen to black people, who have been subjected to centuries of abuse by white people. And stop accusing black people of "reverse racism". Black people can't be racist, because racism requires power, and white people have lorded over black people for centuries. This is what white people do to black people .. [insert examples and research] and this is what you should do about it [insert your ideas]"
I just wrote both off the top of my head. Which do you think will accomplish more in fighting against racism? Which do you think will do more to counter white privilege? Which do you think will cause more division?
My best guess is that the second approach is better suited to people who are naive, already leaning in your direction, already guilt-stricken, or otherwise low-hanging fruit, while the first is better suited to people who are on the fence or skeptical.
I strongly suspect that people who push the "black people can't be racist" rhetoric are blind to this.
To call them "blind" is rhetoric in line with your second example. I would say instead that they disagree with you about which rhetorical strategy is better; they probably have different operational definitions of "better", and different benchmarks by which it is measured. People are complicated. They have explicit goals, and then they have various other motivations that they aren't necessarily even aware of, and others they are aware of but keep hidden. I see that in this subforum in practically every thread. People speak to persuade, to inform, to vent their feelings, to gain status, all sorts of things.
I am starting to suspect that defeating white racism is not their goal.
I doubt it's their only psychological motive, but it may well be the only goal of which they are consciously aware.
A rational person would not demand division or parade prejudice and tribal impulse to combat those very things.
This site should be sufficient evidence that rational people stop being rational when the topic of discussion becomes politics. It seems to me that tribal impulse is one of the main motivators of political discourse. To decry it categorically would open most participants up to justified accusations of almost never practicing what one preaches. To avoid the hypocrisy and actually avoid siding with one tribe or another would relegate one to the irrelevant sidelines of most political discussions(as most are about two teams scoring points against one another, not uncovering the truth and reaching solutions), which would undermine one of the motives underlying communication (attention).