Should gay ism and lesbianism be legalized?

Yes, and it is actually already legal in the US and most countries in the world. The only countries where it is illegal are:

Afghanistan

Algeria

Angola

Antiqua and Barbuda

Bangladesh

Barbados

Belize

Bhutan

Botswana

Brunei

Burundi

Cameroon

Cook Islands

Dominica

Eritrea

Ethiopia

Gambia

Gaza

Ghana

Grenada

Guinea

*Guyana

Iran

Iraq

Jamaica

Kenya

Kiribati

Kuwait

Lebanon

Lesotho

Liberia

Libya

Malawi

Malaysia

Maldives

Mauritania

Mauritius

Morocco

Mozambique

Myanmar

Namibia

Nauru

Nicaragua

Nigeria

Oman

Pakistan

Palau

Papua New Guinea

Qatar

Saint Kitts and Nevis

Saint Lucia

Saint Vincent and the Grenadines

Sao Tome and Principe

Saudi-Arabia

Senegal

Seychelles

Sierra Leone

Singapore

Solomon Islands

Somalia

Sri Lanka

Sudan

Swaziland (female/female-unclear)

Syria (female/female-unclear)

Tanzania

Togo

Tonga

Trinidad and Tobago

Tunisia

Turkmenistan

Tuvalu

Uganda

United Arab Emirates

Uzbekistan

Western Samoa

Yemen

Zambia

Zimbabwe

Countries Whose Laws do not Explicitly ban Same-Sex Behavior, but have some laws which have been used to punish gay and lesbian behavior:

Costa Rica

Democratic Republic of Congo

Egypt

Indonesia

Russia