Expanding on last week's announcement that Wimbledon and the preceding grass-court events would be the first individual tennis tournaments to bar players from the two countries, Hewitt said the club was left with only two options – an outright ban or forcing players to sign declarations condemning the invasion of Ukraine.
"After lengthy and careful consideration, we came to two firm conclusions. First, even if we were to accept entries from Russian and Belarusian players with written declarations, we would risk their success or participation being used to benefit the propaganda machine of the Russian regime, which we could not accept.
"Second, we have a duty to ensure no actions we take should put players or their families at risk. We understand and deeply regret the impact this decision will have on all the people affected.
"But we believe we have made the most responsible decision possible in the circumstances, and there is no viable alternative within the framework of the government's position to the decision we have taken in this truly exceptional and tragic situation."
The WTA and ATP have both criticised Wimbledon's decision and are holding meetings in Madrid this week to decide how to react, with removing ranking points from the tournament a possibility.
Chief executive Sally Bolton said they were in daily communication with the tours, adding: "We won't be speculating on what may or may not happen in the future.
"We continue to make the case for why we have made the decision we have made and the unique set of circumstances we find ourselves in here in the UK. They absolutely appreciate that."
Bolton also revealed that discussions are ongoing with the government regarding Russian and Belarusian coaches and other officials, while Russian media outlets will also be banned but spectators and club members from the two countries will be welcomed.
Leading Russian player Andrey Rublev called the decision "complete discrimination", but Wimbledon refuted that accusation, with Hewitt saying of the player body: "We hope in time they can understand our desire to achieve a responsible outcome. It is not discrimination in the form that is being said."
On the accusation that Wimbledon has not taken similar action in the face of unpalatable actions from other countries, and that this could set a difficult precedent, Hewitt added: "I hear the argument obviously and that is one of the reasons why we took very careful consideration as to whether this was the right course of action.
"We truly believe this is an exceptional situation: first, we have an invasion of a sovereign state with the scale and severity that it has. We have condemnation by over 140 nations through the United Nations. And, in our case, we have specific and directive guidance to address matters."
Lawn Tennis Association chairman Lord Davies, meanwhile, will be welcome at the tournament despite also being chairman of a Russian-owned firm sanctioned by the government.
Hewitt said: "I'm not going to comment on his position but, in terms of is he welcome here? Yes, he is. Our decision is in relation to players only and their participation in Wimbledon and how that is presented."