When a church is shown how far it has drifted from the New Testament, the answer usually comes fast. "No church is perfect. People are flawed." Then come the examples. David took another man's wife. Samson broke his vow. Israel went after idols for centuries. If God's own people were like that, we shouldn't expect too much of the church.
It sounds humble. The mistake under it is that nearly every example comes from before Jesus came.
What they didn't have
The Spirit came upon the Old Testament saints for a task and could leave them. The Spirit of the LORD came mightily upon Samson (Judges 14:6), and later he wist not that the LORD was departed from him (16:20). The Spirit of the LORD departed from Saul (1 Samuel 16:14). David prayed, take not thy holy spirit from me (Psalm 51:11). There were a few exceptions, like Joseph and Joshua, but Moses' wish shows what ordinary Israelites lacked: Would God that all the LORD's people were prophets, and that the LORD would put his spirit upon them! (Numbers 11:29).
The nation had the law as a shadow of good things to come, and not the very image of the things (Hebrews 10:1), read under a veil which vail is done away in Christ (2 Corinthians 3:14). Hebrews ends its list of the faithful by saying God having provided some better thing for us, that they without us should not be made perfect (Hebrews 11:40). And Paul tells us what their failures are for: they are written for our admonition (1 Corinthians 10:11). The excuse treats that warning as a permission slip.
What we have
We've seen him. No man hath seen God at any time; the only begotten Son... he hath declared him (John 1:18). He is the express image of his person (Hebrews 1:3). We watched how he treated God, the sinner, the outsider and the poor, and he told us to copy it. For I have given you an example, that ye should do as I have done to you (John 13:15). He that saith he abideth in him ought himself also so to walk, even as he walked (1 John 2:6).
The Spirit dwells in every believer. He dwelleth with you, and shall be in you (John 14:17). Your body is the temple of the Holy Ghost which is in you (1 Corinthians 6:19). Ezekiel said what that would do: I will put my spirit within you, and cause you to walk in my statutes (Ezekiel 36:27).
And the pattern has been delivered. God hath given unto us all things that pertain unto life and godliness (2 Peter 1:3). Paul taught his ways every where in every church (1 Corinthians 4:17).
More given, more required
Jesus spelled out what this does to excuses: If I had not come and spoken unto them, they had not had sin: but now they have no cloke for their sin (John 15:22). For unto whomsoever much is given, of him shall be much required (Luke 12:48). Hebrews reasons from Israel's failures to a stricter standard for us: How shall we escape, if we neglect so great salvation (Hebrews 2:3). The excuse runs the Bible's logic backwards, from their failures to a looser standard.
Perfect means grown up
The word perfect in the New Testament, teleios, means mature, full-grown. Paul says he isn't yet perfect, then in the same breath tells the perfect to keep pressing on (Philippians 3:12-15). Jesus' command to be ye therefore perfect (Matthew 5:48) comes right after his teaching on loving enemies, which makes it a standard for how a church treats people. John holds the standard and the mercy together without letting grace lower the goal: these things write I unto you, that ye sin not. And if any man sin, we have an advocate (1 John 2:1).
Flawed people, chosen structures
The excuse blurs weakness and structure together. Personal weakness is real, and grace covers it. But nobody stumbles into a payroll. Nobody falls into a building programme in a moment of temptation. The shape of a church is decided in meetings, budgeted and kept, year after year. "People are flawed" can explain why a deacon was unkind on Tuesday, but not why a church keeps a structure the New Testament never gave it after being shown the pattern.
Corinth was as flawed as a church can be, and Paul never told them no church is perfect. His answer was the rest will I set in order when I come (1 Corinthians 11:34). Jesus told Ephesus to repent, and do the first works; or else I will come unto thee quickly, and will remove thy candlestick (Revelation 2:5). And the design itself was built for flawed people: Matthew 18 for the brother who trespasses, Galatians 6:1 for the man overtaken in a fault, plural elders because one man alone goes wrong. So the flaws the excuse points to are the reason to keep the design.
It has been done. The church in Jerusalem had Ananias and Sapphira and the neglected widows, and it kept the pattern and used it to fix what was wrong (Acts 5-6). Thessalonica was a young church of former idol-worshippers, and Paul could write, ye yourselves are taught of God to love one another (1 Thessalonians 4:9).
None of this is a club for beating people. Restore such an one in the spirit of meekness; considering thyself (Galatians 6:1). But the grace of God that brings salvation is teaching us that, denying ungodliness and worldly lusts, we should live soberly, righteously, and godly, in this present world (Titus 2:11-12). A grace that teaches us to live the pattern can't be the thing that excuses us from it.