By “unscriptural,” I assume you mean that which contradicts Scripture. How does praying to Mary or angels contradict Scripture? Praying to either is a form of asking them to pray for us as we would ask a friend to pray for us.
The attempt to sanction praying to saints in glory is based upon the lack of a specific condemnation of it, and an appeal to communication in the earthly realm, as well to motive and pathos. However, this is the type of exegesis which homosexuals attempt, namely, that even if the Bible only establishes one type of sanctified union, then it does not mean God excludes another, even if He condemns broadly condemns it in type. They also invoke equality in spiritual relations (Col. 3:28) to negate physical distinctions, and suppose that motive sanctifies a basic practice which is never established as approved.
In examining the issue of praying to departed believers (saints), we see that,
1. the Bible broadly condemns forms of seeking contact with the dead, (Lev. 19:31; 20:6-7,27; Dt. 18:10,11; Isaiah 8:19) (which is why Saul had to go to a witch to do so. (1Sam, 28:6,7)
Those who do demand an explicit specific injunction against a practice which is only sanctioned with one particular type of object could also sanction things such as consensual cannibalism as a practice. (Gn. 9:2,3) While certain distinctions may be made versus regards necromancy and the like, such as that the ultimate object of praying to saints in Heaven is God, versus demons, we also see that,
2. the only object of prayer in the Bible - and there are a lot of prayers in the Bible - (http://peacebyjesus.witnesstoday.org/BIBLE-PRAYERS.html) is God, the Father and the Son, and in no place is praying to anyone else sanctioned or exampled. The Lord’s own instruction on prayer set forth the Father as its object,
“And he said unto them, When ye pray, say, Our Father which art in heaven, Hallowed be thy name..., (Lk. 11:2) “when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father” (Mt. 6:6) He further clearly establishes that only through Him can men come to the Father, (Jn. 14:6) and in so doing men are to salvifically call upon Christ, (Rm. 10:12,13; Joel 2:32) and pray and give thanks. (Acts 7:59; Rm. 1:8; 1Cor. 1:2; Eph. 2:18)
3. The sufficiency of God as the Object of prayer is due to Divine incommunicable attributes, that of His omniscience, and also in the case of Christ, His being “in all points tempted like as we are, yet without sin.” Jesus Christ is singularly exalted as man’s ceaseless and always available intercessor, (Heb. 4:14-16; 7:25) who declares He stands at the door of one’s heart, to come in and commune with man. (Rev. 3:20) This is written to a church which should be looking for compassion, yet neither here nor in any other place is it even intimated that men should not or cannot come directly to Christ in prayer who is set forth as man’s only heavenly intercessor. (1Tim. 2:5)
4. Praying to humans in Heaven, who are expected to be able to hear billions of prayers at once, ascribes attributes of Divinity to them, and also infers that either God needs help in this business, and or that they are more able intercessors. The latter is especially what is conveyed in exhortations to come to Mary, but who was not “in all points tempted like as we are, yet without sin”, nor is omniscience ascribed to such.
As for equating such petitioning with earthly relations, this analogy is problematic, as this presumes a degree of correspondence btwn humans relations in the physical earthly realm and that of the spiritual realm, but in which there are critical distinctions, as what is ordained for for relations btwn humans in the physical realm does not necessarily apply to the spiritual realm, as in marriage. (Mt. 22:29,30).
Also, communication btwn humans on earth, such as in asking for help, is not to be done directly between them by means which are purely spiritual or telepathic (ESP), which is God’s realm - and that of the devil - but articulate communication is to be restricted to the use of human means (words, body language, senses) which God has ordained.
In contrast, spiritual prayer communication to the spiritual realm of Heaven is sanctioned, but again, only to God in Heaven. There is simply no need at all to pray to anyone else in Heaven but the Lord, nor sanction or even one example for praying to anything but Him - an conspicuous omission by the Holy Spirit and an inconceivable one if such a basic practice for which sanction is presumed - thus no warrant to sanctify what was a pagan practice. This evidences an accommodation of paganism, and an exaltation of men above that which is written, (1Cor. 4:6) and which impugns th full honor due to Christ.
Heb 2:18 For in that he himself hath suffered being tempted, he is able to succour them that are tempted.
Hebrews 4:14-16 Seeing then that we have a great high priest, that is passed into the heavens, Jesus the Son of God, let us hold fast our profession. (15) For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin. (16) Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need.
Hebrews 7:25 Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them.
Psa 62:8 Trust in him at all times; ye people, pour out your heart before him: God is a refuge for us. Selah.
Isa 55:6 Seek ye the LORD while he may be found, call ye upon him while he is near: