Ps. 145:9 The LORD is good to all: and his tender mercies are over all his works.
Against this verse, critics might cite any number of verse where God is "not good" or merciful to people -- laying judgment on them, for example.
The simplest answer is to note that Psalm 145 is a hymn of praise to God. This by itself is enough to resolve the problem, because hymns, poems, and proverbs are not to be taken as absolutes.
But let's go further anyway. Verses 8-10 and 20 are all we need to establish the context:
Ps. 145:8-10 The Lord is gracious and compassionate, slow to anger and rich in love. The Lord is good to all; he has compassion on all he has made. All you have made will praise you, O Lord; your saints will extol you.
Ps. 145:20 The Lord watches over all who loves him, but all the wicked he will destroy.
God is good to all, but when one of those "all" turn wicked, they open themselves up for God's anger, as is the case in many places in the Bible. Here's one example we've seen cited:
Jer. 13:14 And I will dash them one against another, even the fathers and the sons together, saith the LORD: I will not pity, nor spare, nor have mercy, but destroy them.
The critic will say God wasn't being merciful or good here, but the people of Judah are prior to this verse declared wicked (Jer. 13:10) and subject to God's judgment and wrath. This fits in with the context of the Psalm.
To use an earthly illustration, even when our parents punish us, we don't stop saying that they are good to us. Castigation and discipline are an element of good parenting. On the higher level of the relationship between God and man, Psalms indicates the God is "slow to anger" - we get plenty of chances to repent and retain God's good graces.
But to use that example from Jeremiah, those whom Jeremiah addresses, the corporate nation of Judah, had been involved in wickedness for quite some time with no sign of repentance. Their wickedness was to the point where judgment was required.
By reading Psalms 145:9 isolated from its context, and genre as an ancient hymn, Skeptics read into it a God who would have to NEVER react against evil.