Having a closed hearing and locking out the other party is not right regardless of which party is doing it. They're trying to impeach Trump by having a secret trial where only the prosecutor is allowed to make his case. That's un-American.
There are 40-some Republicans on the three committees of the impeachment inquiry--and this is "locking out?" And this is, in essence, a grand jury process where, YES, only the prosecutor makes their case as has always been true. It's not a trial, guilty/not guilty, it's a determination if there is enough evidence to charge the person and bring him to trial where guilty/not guilty will be decided.
It's astounding and depressing how many people are totally ignorant of the constitution and the workings of the legal system.