You are caught up in a slippery slope fallacy. http://en.wikipedia.org/wiki/Slippery_slope
'If some chapters flirt with the limitation by taking a few lances, then all chapters will have all lance ships, and will build a fleet that will rival the IN'
They are certainly a long way from that, currently, with only about 12 capital ships in a chapter.
Marines can make escorts, but not capital ships, or at least there is nothing written about it.
There is rarely a 'line in the sand' in the Imperium, rather a hazy field where, depending on whose in charge of the situation, a decision is made at some point. And a few lances does not an inquisitorial appointment make, read the fluff that has been quoted to you, and it will be clear.
Your current argument is 'Tell me one reason marines would have lances' To which there is a reply, reasons are given, and you reply with 'Tell me one reason why marines would have lances.'
What is the difference between lance escorts and lances on a small percentage of capital ships?
DO YOU REALIZE MARINES ALREADY HAVE AND USE LANCES?
If you keep referring to the psycology of the Imperium, you must know, as I said in earlier posts, that it is incredibly inefficient and contradictory.
Read the reasons given if you feel like it, or give me something besides opinion and conjecture.