From my point of view, people are angry at ICE not mainly because deportations exist, but because of the methods being used, and those methods are clearly encouraged from above. Who else would be responsible, if not the policymakers themselves?

You can argue about whether immigration was a real problem or mostly fearmongering. In that case, any realistically achievable level of deportations under the previous administration would probably have been dismissed as insufficient anyway so the outcome would the same. But if policymakers deliberately loosen rules, they can be blamed for the consequences.

It is no different from weakening medicine purity standards and then acting surprised when people die. In that case, responsibility clearly falls on the people who made the policy too.

It may sound blunt, but assigning blame is a normal part of politics. Politicians are there to make decisions, and they should be praised or blamed for the results.