Overstatements such as these can undercut an argument. Technically, the sentences above are wrong, not so much because their authors don't understand the nature of the past but because they went too far in the right direction.
If, for example, you say "All Romans loved their state always!" and if I can think of a single exception, some Roman who only liked but didn't love his state—Nero, perhaps?—then your statement is, strictly speaking, incorrect. And was there not one single ancient Greek who preferred barbarians to his own kind? How about Alexander the Great? So then did Socrates never give a simple lecture without questioning people? What about at his trial, as recorded in Plato's Apology, where the court officials expressly forbade any philosophical cross examination on his part?
The moral here is "Don't overstate your case." Back off a little. Say, instead, "Most Romans felt a strong commitment to their state." "On the whole the ancient Greeks hated outsiders." "Socrates preferred to guide others to an understanding of his philosophy by questioning them rather than telling them explicitly what he thought." The point remains the same, but the statement is now technically correct. And whatever exceptions exist are just that, exceptions. So, as a general rule avoid "all," "always," "completely," "never," "only" and any word that backs you into a corner with no way out.