This is from the long-running anime Sazae-san. Let me set up the situation. A young couple is at a public telephone. The woman is calling her parents, telling them that she's at her female friend's and will get home late today. The viewer sees that this is a lie (since she's with her boyfriend and the guy is sticking his tongue out). Then suddenly, a stranger out of nowhere （波平）just snatches the phone from her hand and seems to be giving the parents a lecture. Below is the transcript:
(The woman) もしもし？
(The woman) 今 カズコんちにいるの。
(The woman) 帰り 遅くなるから。
（波平）いかん！ (snatches the phone)
（波平）あなた お母さんですか？(already talking on the phone)
(The woman's mother, on the phone) あの ちょっと
(The woman's mother, on the phone) 主人と代わります。
The anime is here (starting at 10:30): http://www.dailymotion.com/video/x46ojrm. Watching it is going to be essential in understanding the situation, I think.
Now my question is, what is 波平 saying to the parents? It seems to me that he says to them that they are raising their girl wrong (お宅の教育は 間違っている)? The last part I simply don't understand: "かたいことばかりは言えないがだ". Something about them being too conservative? Also, what's with "がだ" at the end? Doesn't look correct grammar-wise. (This script comes from TV feed so it should be correct). This is all weird: I thought he would tell the parents the truth (that they were being lying to), and not go at them like this (perhaps I misunderstand the scene?).