Contrast this with the Clinton impeachment hearings - where it was open to all representatives, and Clinton had his own lawyers present to cross examine witnesses.
Yes, these are secret - because the testimony is not known to anyone who isn't allowed in the hearing, nobody is "allowed" to discuss the testimony...but somehow the things they think hurt POTUS magically leak out....every day....like clockwork.
Who are the witnesses, what is their relationship to POTUS, is their information first hand or hearsay, do they have political motivations.... All of these things are probed in cross examination, which is why Schiff doesn't want it public.
In previous impeachment hearings, all members were allowed to be present - because the 22 members of the house intelligence committee represent only 5% of the people of the US. Representatives of 95% of WE THE PEOPLE are locked out of the hearings - and may be expected to vote with no access to that information.
This is also, normally, handled by the house judiciary committee - which seems to have a better grasp on legality than the house intelligence committee.
Everything about this is wrong.