Why aren't Roosevelt and Churchill loathed for signing agreements with genocide Stalin?

Sir Winston Churchill was an amazing man & Army officer who was responsible, along with a team of British lawyers, for the introduction of the great Charter of Human Rights, later known as the European Convention on Human Rights. It protects the right to life, liberty, security, free speech, fair trial, free & fair elections, freedom from torture, slavery & discrimination ✍🏻⚖️👊🏻

There other acts redeemed their mistakes.

Well, Germany had instigated two world wars in two generations. Anything else must have looked better by comparison.