Behavior we don't understand
ד"א הלה' תגמלו זאת - משל לאחד שהיה עומד וצוהב כנגד אביו.
אמר לו: שוטה שבעולם! כנגד מי אתה יושב וצוהב, כנגד אביך? שמע כמה עמל עמל בך, וכמה יגיעה יגע בך, אם לא כבדתו לשעבר - צריך אתה לכבדו עכשיו, שלא יהיה כותב כל נכסיו לאחרים!
כך אמר להם משה לישראל: אי אתם זכורים נסים וגבורות שעשה לכם המקום במצרים? הזכרו כמה טובות שעתיד ליתן לכם לעולם הבא:
Variantly: "Would you thus requite the Eternal?" An analogy: one is standing and taunting his father.
A bystander: Who are you taunting? Your father? How much toil did he expend on you! How much strength! If you did not honor him in the past, (at least) you should honor him now, so that he not write over all of his holdings to others!
Similarly, Moses said to Israel: If you do not remember the miracles and mighty acts that the Eternal performed for you in Egypt, (at least) be mindful all the good that God is destined to bestow upon you in the world to come (if you heed God's word).
The issue at hand is gauging the individual's evidence of understanding. If the rabbis could not discern an individual's level of understanding, that person was disqualified from serving as a witness and (potentially) exempt from observance of certain commandments.
תָּנוּ רַבָּנַן: אֵיזֶהוּ שׁוֹטֶה? הַיּוֹצֵא יְחִידִי בַּלַּיְלָה, וְהַלָּן בְּבֵית הַקְּבָרוֹת, וְהַמְקָרֵעַ אֶת כְּסוּתוֹ. אִיתְּמַר, רַב הוּנָא אָמַר: עַד שֶׁיְּהוּ כּוּלָּן בְּבַת אַחַת, רַבִּי יוֹחָנָן אָמַר: אֲפִילּוּ בְּאַחַת מֵהֶן.
The Sages taught: Who is considered a שׁוֹטֶה? One who goes out alone at night, and one who sleeps in a cemetery, and one who rends his garment. It was stated that Rav Huna said: One does not have the halakhic status of a שׁוֹטֶה until there are all of these signs present in him at the same time. Rabbi Yoḥanan said: He is considered a שׁוֹטֶה even due to the appearance of one of these signs.
החובל בחרש שוטה וקטן חייב.
The one who injures a deaf-mute, שׁוֹטֶה, or a child is liable [for damages].
Mental Retardation, Group Homes and the Rabbi YD 336:1.2000 Tesuvah: Committee on Jewish Law and Standards (Rabbinical Assembly, Conservative)
"Clearly, the שׁוֹטֶה is a highly subjective category requiring individual assessment. Some people with mental retardation at the severe or profound levels may, indeed, display some of the classic disoriented behavior of the שׁוֹטֶה. Others will be best viewed as פתיים, those of significantly diminished intelligence. Both are at a societal disadvantage and require concerted efforts to attain integration into the culture at large."
Those who are considered a שׁוֹטֶה may not be able to project the same level of understanding [in the ancient world] but they are still capable of understanding a certain level of harm or mistreatment.
Asking for help is encouraged!
הַשּׁוֹטֶה אֵין מִקָּחוֹ מִקָּח וְאֵין מִמְכָּרוֹ מִמְכָּר וְאֵין מַתְּנוֹתָיו קַיָּמוֹת. וּבֵית דִּין מַעֲמִידִים אַפּוֹטְרוֹפּוֹס לְשׁוֹטִים כְּדֶרֶךְ שֶׁמַּעֲמִידִין לִקְטַנִּים:
Neither a sale nor a purchase involving a שׁוֹטֶה is binding, nor are the presents he gives effective. Instead, the court must appoint a guardian for such a person, just as it appoints guardians for minors.
Who is the court in the 21st century? The Jewish community! Rabbinically, just as the court takes on responsibility for ensuring a child is circumcised, receives and education, etc, it is the community's response to ensure the child has the support they need.
Give them a chance!
קָטָן עַד שֵׁשׁ שָׁנִים אֵין הַקְנָיָתוֹ לַאֲחֵרִים כְּלוּם. וּמִשֵּׁשׁ שָׁנִים עַד שֶׁיַּגְדִּיל אִם יוֹדֵעַ בְּטִיב מַשָּׂא וּמַתָּן מִקָּחוֹ מִקָּח וּמִמְכָּרוֹ מִמְכָּר וּמַתְּנָתוֹ קַיֶּמֶת.
...
וְדָבָר זֶה מִדִּבְרֵי חֲכָמִים כְּמוֹ שֶׁבֵּאַרְנוּ כְּדֵי שֶׁלֹּא יְבַטֵּל וְלֹא יִמָּצֵא מִי שֶׁיִּמְכֹּר לוֹ וְלֹא יִקַּח מִמֶּנּוּ. וְהַכּל בְּמִטַּלְטְלִין אֲבָל בַּקַּרְקַע אֵינוֹ מוֹכֵר וְלֹא נוֹתֵן עַד שֶׁיַּגְדִּיל:
The following rules apply to a minor: Until he is six years old, he may not transfer property to others at all. From the age of six until he attains majority, he should be tested. If he possesses an understanding of the nature of financial transactions, any purchases or sales he undertakes, and any presents he gives, are binding.
What is our intended outcome?
ר' יהודה סומא מכל המצות מ"מ מדרבנן חייב דאע"ג דאשה מיפטרא במצות עשה שהזמן גרמא ולא מחייבינן אפילו מדרבנן משום שיש מצות הרבה דמחייבת בהו אבל סומא אי פטרת ליה מכל המצות אפי' מדרבנן א"כ ה"ל כמו נכרי שאין נוהג בתורת ישראל כלל
[loose translation] In the words of Rabbi Yehudah: If you exempt the blind from the requirement to observe all the commandments, even if this requirement is rabbinically-imposed, you make him as though he is a Gentile, who does not walk in the path of Judaism at all.
What should we do?
(ל) מי שיש לו מום בפניו או בידיו ... לא ישא את כפיו מפני שהעם מסתכלין בו וה"ה למי שיש מומין ברגליו במקום שעולים לדוכן בלא בתי שוקיים וכן מי שרירו יורד על זקנו או שעיניו זולפים דמעות וכן סומא באחד מעיניו לא ישא את כפיו ואם הי' דש בעירו דהיינו שהם רגילים בו ומכירין הכל שיש בו אותו מום ישא כפיו ואפי' הוא סומא בשתי עיניו.
(30) One who has an deformity on his face or his hands, ... should not perform the priestly blessing because the congregation will stare at him. And the same applies for one who has an deformity on his feet, in a place where they ascend to the platform without socks. And so too one who has spittle/mucus drooling down his beard, or if his eyes tear up, and similarly, one who is blind in one of his eyes; [all these] should not perform the priestly blessing. However, if he is "broken in" [well-known] in his city, meaning that they are familiar with him and everyone recognizes that he has this deformity, he may perform the blessing, even if he is blind in both eyes.