This seems to be the most audacious claim yet I have heard yet about the negative effects of any yoga program. Any technique is only a tool to discover your own insides, and any technique if it cant enlighten you, surely cant by itself cause ‘negative mindset’ in you.
Having done various programs from various groups including Osho, Art of Living, Isha Foundation, I have the highest praise for all of them. They are all, especially Isha Foundation and Art of Living, volunteer run organizations, where full time working people like yourself volunteer and facilitate the classes, for no other accolade but to spread the inner tools that transformed their lives to others as well. Learning a multidimensional alive technique like Yoga through just books like you recommend is the worst advice ever. Any Yogi would tell you that. Leave yoga, any complex technique, be it dance, martial arts, is best learnt in person by a dedicated, devoted teacher and even better in a group! Buddha talked so much about ‘Sangha’, a group of people walking on the same path, their combined energy helps each one of them. Before buying into such negative baseless chatter it’ll be best to discover these programs for yourself, see the devotion, sincertity of the teachers, who conduct them, the content of the programs and the journey they take you through, before just dismissing anything as a ‘cult’. And regular practice correction sessions happen even for Isha meditators I have heard in all metropolitan cities, where they would be happy to hear and sort out any of your problems.