As others have said elsewhere, you may be breaking the terms and conditions of a pay to view site. You may also be breaking copyright. Ancestry and other sites pay to host these images. Sometimes, they may provide the services necessary for producing the images (and hence pay a reduced or no licence fee). These licence fees provide much needed income to the archives who hold the original documents. Moreover, I would find it much more expensive to visit the various archives to see the original records. Paying a subscription is far less than regular travel costs to even a nearby archives. I do use my local archives but not every day. I also sometimes use other local archives and the National Archives to use records that are nowhere on line. These visits can be extremely expensive so are occassional.(travel, food, hotel costs)
My subscriptions allow me to see records that would be otherwise unavailable to me. I'll cite them in full and also transcribe records (I've transcribed a large number of wills available on ancestry and placed them in wiki-tree).However, I refuse to break the terms and conditions of my subscription which in many cases it would also contravene copyright .
In many ways, It would be contrary to my own interest. If everybody did it this, there would be no profit for these companies in providing the service. If they did not make a profit they wouldn't provide the service.Local and National archives in the UK (and probably elsewhere) would also not derive the income from these companies that helps preserve and make accessible many other, less popular records
Here's an example of copyright details on Ancestry for the 1881 census of England and Wales ( these images are not on any free site, Family Search has partial transcripts)
Original data: Census Returns of England and Wales, 1881. Kew, Surrey, England: The National Archives of the UK (TNA): Public Record Office (PRO), 1881.
Images © Crown copyright. Images reproduced by courtesy of The National Archives, London, England.
Images may be used only for purposes of research, private study or education. Applications for any other use should be made to The National Archives Image Library, Kew, Richmond, Surrey TW9 4DU, Tel: 020 8392 5225 Fax: 020 8392 5266.
Here's another set of records. This time for the Freedom of the City of London Admission papers. (I don't think these are available elsewhere unless you visit the Archives in London.)
Published in March 2010 by
London Metropolitan Archives (address, telephone number and email in original)
©London Metropolitan Archives
Except as otherwise permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted in any form or by any means, with the prior permission in writing of the publisher, or in the case of reprographic reproduction, in accordance with the terms of a licence issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the London Metropolitan Archives at the above address