I'm living in Israel for 10 years as an American citizen, and don't have any plan on ever making citizenship. Too many potential problems, and I can get almost all the benefits with a student visa that Israeli citizens can get. You can even get a student visa with permission to work (a new thing from 5 years ago), so anyone who learns part time can really get a student visa.
There is no reason to keep it, except for some minor things like free tourist visa for Israelis to russia vs. the $180 fee for US citizens. You can always reapply for citizenship if you ever move to Israel and want it. See
http://www.coolideaz.com/2015/08/citizenship-be-gone.html He describes the whole process and his experience renouncing citizenship. I recommend doing it ASAP, since the government is actively trying to force chareidi draft, through stages, and may make it much more difficult to renounce in the future. Also , each renouncement application has to be reviewed by the Minister of the Interior, currently Aryeh Deri, who I would not expect to be too stubborn about it. The government and ministers may change soon.
"For the record, a revoked citizen can have a big problem getting a student visa in Israel." Nonsense, I never heard of any problem like that.
There may be a misunderstanding between "revoked" and "renouncing". A person whose citizenship is revoked is usually due to terrorism, etc., and can understandably have problems getting a visa. Though I hope nobody here has that problem!
Renouncing is declaring the want not to be a citizen, for instance, due to permanent residence being abroad without any plan of coming back as a citizen.
This would not be interpreted as hostile to Israel, so there should be no problem getting a student visa, to the contrary, Israel would want to issue a visa, hoping that the student will settle in israel and eventually want to become a citizen again.
Is your son really an Israeli citizen or was he just born in israel to foreign parents? A child born to foreign parents does not get automatic citizenship. This is how the law has been for about 20 years.