He committed espionage.
It doesn’t matter if he did it for altruistic reasons (i.e. - he wanted to help Israel).
He was in a position of responsibility and chose to betray his nation.
The only reason he’s not doing life in prison (like Aldrich Ames and Richard Hanssen) is because Israel was an ally and the secrets he revealed didn’t rise to level of those Hanssen and Ames gave away.
I'm not sure the latter statement is true. Pollard gave away a vast volume of classified documents. I've heard that these included the very top secrets of signals intelligence. Probably it can't even be stated what he stole. Evidently the people who know think that it is so serious that he should not be freed even if it helps achieve peace in the Middle East.
Also it's not clear that Pollard was acting altruistically (as if that would be an excuse). IIRC he was selling documents to other countries such as South Africa and he was paid by Israel.
Also the fact that Israel is an "ally" is not that relevant since once they had all our secrets they traded them to other countries such as the Soviet Union to achieve their own interests, which are not always the same as ours. No matter what Pollard's motives, he grievously harmed the United States.
One of the reasons that there is so much pressure from Israel to free him is that Israel wants to send a signal to all their potential spies that they will never be abandoned. Also this seems to have become a domestic political issue in Israel. But the US should be concerned about about the message we are sending to potential traitors and spies.
His motivations may have been, in part, his allegiance to Israel.
But he also wanted (and accepted) MONEY for those valuable secrets.
To Israelis he may well be a hero. To Americans he will always be a traitor and a spy.
I am an American.