People are tinkering with phones in order to circumvent law and make quick, short term profit at the cost of tax paying citizens. None of the noble reasons you'd think of apply.
You're overgeneralizing. A company has a limited amount of employees that are working full time. Meanwhile the millions of people who install ROMs may spend a week tinkering and then it's over for them. The chance that a few thousand of them become interested in making their own ROMs (and therefore become software engineers) will become zero thanks to this law.
Governments should not enforce international trade agreements on the off-chance that someone somewhere might have an epiphany while installing illegal software? No.
I would appreciate if you provide a definition of illegal that doesn't amount to "prohibited by law". In this case, the set of laws that are placed in order to protect international trade agreements.
These are pretty bold points that would deserve to be expanded, as they cover everyone doing non-standard things with their hardware or even just changing their battery. The whole statement sounds like a "think of the children"-style argument to me.